SPECIAL ISSUE
Dolomitic slates from Uruguay: petrophysical
and petromechanical characterization and deposit evaluation
Manuela Morales Demarco • Pedro Oyhantc¸abal •
Karl-Jochen Stein • Siegfried Siegesmund
Received: 22 March 2012 / Accepted: 16 August 2012 / Published online: 4 September 2012
 The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract Slates are internationally known as roof and
fac¸ade-cladding material since prehistoric times. The
methods required to mine and manufacture these dimen-
sional stones are relatively simple in comparison to those
utilized in granitic dimensional stones. This has led to a
worldwide rentable commercialization of slate in the last
centuries and also to the development of characteristic
cultural landscapes. In Uruguay several slates are mined
and used in architecture, especially as fac¸ade cladding and
floor slabs. The most important slates regarding their pro-
duction and utilization are the dolomitic slates. These
dolomitic slates are associated with the Neoproterozoic
thrust and fold belt of the Dom Feliciano belt. Represen-
tative samples have been geochemically and petrogra-
phically characterized, as well as petrophysically and
petromechanically analyzed. The petrophysical and petro-
mechanical properties were investigated in a very system-
atic way with respect to the new European standards,
showing values comparable to those registered for inter-
nationally known slates. Detailed structural and deposit
analysis were carried out in Uruguay in order to evaluate the
dolomitic slate deposits. The slates are linked to calc-sili-
cate strata in a greenschist facies volcano-sedimentary
sequence and the deposits are located in the limb of a
regional fold, where bedding and cleavage are parallel. The
main lithotype is a layered and fine-grained dolomitic slate
with a quite diverse palette of colors: light and dark green,
gray, dark gray, reddish and black. The mined slate is split
into slabs 0.5–2 cm thick. In the past, the average produc-
tion in Uruguay was around 4,000 tons/year and a historical
maximum of 13,000 tons was reached in 1993 (Oyhantc¸a-
bal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The
oscillations in the regional demand were the cause of sev-
eral flourishing and decay cycles in the activity, but our
investigation shows a considerable volume of indicated
resources and therefore a very good potential.
Keywords Slates  Dimensional stones  Petrophysical
properties  Petrography  Uruguay
Introduction
Over the millennia slates in a broader sense have been one
of the most favorite dimensional stones because of their
particular attributes, such as fissility in a preferred direction
and their high strength. Different shapes can be produced
by simple technical means for roof and fac¸ade cladding
(Fig. 1a), as well as for everyday objects and floor con-
solidation. Slate tablets and chalk (Fig. 1b) are one of the
most important precursors to the personal computer, to
which several generations owe their education in the
acquisition of writing and mathematical skills.
Slate has been used as a roof-cladding material since
Neolithic times (Card 2010). In regions where this resource
was easily mined, the widespread application of slates in
constructions resulted in the development of characteristic
cultural landscapes. The traditional slate roof cladding has
M. Morales Demarco (&)  S. Siegesmund
Geoscience Center of the Georg-August University Go¨ttingen,
Goldschmidtstrasse 7, 37077 Go¨ttingen, Germany
e-mail: manugea@gmail.com
P. Oyhantc¸abal
Departamento de Geologı´a, Facultad de Ciencias,
Universidad de la Repu´blica, Igua´ 4225,
C.P. 11400 Montevideo, Uruguay
K.-J. Stein
Natursteininformationsbu¨ro, Am Schulzensee 3,
OT Waldsee, 17258 Feldberger Seenlandschaft, Germany
123
Environ Earth Sci (2013) 69:1361–1395
DOI 10.1007/s12665-012-1921-7
1362 Environ Earth Sci (2013) 69:1361–1395
123
been displaced by other building materials since middle of
the twentieth century, leading to a dramatic decline of the
traditional slate industry.
Some rock types (e.g., sandstones, gneisses) also show
fissility and are often sold as slates because they are used in
similar applications (floor slabs, wall cladding, etc.). The
term slate defines a fine-grained metamorphic rock that
underwent low-grade regional metamorphism and pos-
sesses slaty cleavage (Allaby and Allaby 1990; Jackson
1997; Bucher and Frey 2002). This cleavage is defined as a
foliation, which results from the alignment of phyllosili-
cates in response to compressive tectonic deformation
(Allaby and Allaby 1990; Jackson 1997; Bucher and Frey
2002). With respect to the DIN EN 12326-1, a slate is a
metamorphic rock with slaty cleavage formed by the
alignment of phyllosilicate minerals (mainly mica and
chlorite), quartz and other typical minerals. From the
commercial point of view, a slate is a dimensional stone
with a very well-developed fissility, which allows the rock
to be easily split. Afterwards the stone can be manufac-
tured into roofing and cladding slate, or be used in special
cases such as billiard table-tops, laboratory benches, and
blackboards (Allaby and Allaby 1990).
Rocks possessing this property are slates, some gneisses
and phyllites, some limestones, quartzites and fine-grained
pyroclastic rocks. In contrast, fine-grained sedimentary
rocks with a high proportion of clay minerals are defined as
shale. When they are split into thin slabs they are also
commercialized as slates.
When the rock splits along the original bedding the
terms used are ‘‘mass slate’’ or ‘‘parallel slate’’ (from the
German term ‘‘Parallelschiefer’’). When the dominant fis-
sility is defined by a new developed cleavage, the term
‘‘transversal slate’’ (from the German ‘‘Transversalschie-
fer’’) is preferred. The angle between the slaty cleavage
and the bedding can vary and is essentially the result of the
tectonic overprinting.
Prior to the application of new varieties, it is necessary
to analyze the stone petrographically and conduct petro-
physical investigations to ensure a safe use for construction
purposes. In the slate group it is critical to evaluate the
amount of ore minerals (pyrite, chalcopyrite, etc.) and
carbonates. Also petromechanical properties are of partic-
ular relevance, especially flexural strength, as well as water
uptake, thermal behavior and freeze–thaw stability.
Another factor to be taken into account prior to the
application of new slate varieties is the reliability of the
supply. This is related to the fact that some slates are only
available for a short time and only in a few specific formats.
Relying on established commercial varieties will possibly
prevent constructional and technical delivery problems.
In addition to the geology of the deposit, the durability of
the slate plays a decisive role in their possible applications.
The expected economic lifetime of roof and fac¸ade-clad-
ding slate depends on the resistance against environmental
agents, especially weather conditions to which they are
exposed. These include salt attack or freeze–thaw stability
as well as impacts of thermal and hydric variations. Slates
with inclusions, e.g., coarse-grained pyrite, are not very
stable against temperature changes, due to the difference in
thermal expansion among the rock components. This dif-
ferential behavior can lead to a loosening of these inclusions
from slates used for different constructive purposes.
Chemical and biological weathering can be critical for
different types of slates, especially when considering the
relevance of color stability.
In this study, the Uruguayan slates are characterized in
detail based on their petrography and petrophysical prop-
erties. In order to perform a comparison several slates from
Spain, Brazil, Argentina, Portugal and Germany are also
characterized from the petrographical and petrophysical
point of view. Three groups of slates have been defined:
dolomitic, semipelitic and pelitic slates.
Overview of the slate market and slate applications
According to Montani (2008), the main producers of slate
in 2007 were, in order of importance, Spain, Brazil, China,
Canada and India (Fig. 2); together these countries produce
almost 75 % of the world production. Other countries
supplying slate as a dimensional stone are Italy, the USA,
Germany, Belgium, Norway, France, Portugal and Turkey.
The most important consumer is France. Traditional slate
countries in terms of use are also Germany, Benelux and
Great Britain. Uruguay has a relatively large variety of
slates, which are incorrectly described as quartzites
(Comunita` Economica Europea-Uruguay, no date) or chl-
oritic phyllites (Coronel et al. 1987).
A highly appreciated feature typical of slates is their
uniform fabric and, in most of the cases, a deep black color.
Their schistose structure is advantageous and convenient for
mining and processing. Traditionally slates have been used as
roof and fac¸ade-cladding material. The optimization of
modern mining techniques allows the excavation of larger
blocks and better processing. This has led to a greater spec-
trum of products, and therefore, a wider application of slates.
For the design of outdoor areas the new application for
slates includes floor slabs (in various polygonal shapes),
Fig. 1 Typical applications of slates in Uruguay and Germany.
a Roof and wall cladding in Germany using traditional black slate;
b slate tablets and blackboards for writing and drawing; c dry stone
wall of black slate used for a fern bed (Germany); d polygonal floor
slabs of Brazil colored slate and stair trades of black slate (Germany);
e Uruguayan colored dolomitic slates used as wall cladding, note that
the slabs are parallel and perpendicular to the slaty cleavage;
f Uruguayan colored dolomitic slate applied as chimney cladding,
socle cladding and polygonal floor slabs
b
Environ Earth Sci (2013) 69:1361–1395 1363
123
garden and landscaping elements (Fig. 1c), stone stair
treads (Fig. 1d), gabions, stream and spring cladding,
rubble stone and dry stone walls. Even gravestones and
tombs are constructed using slate.
For indoor use several examples include pavements (in
various polygonal shapes), wall cladding, window sills,
marquetry elements for tables and furniture, as well as gift
items (watches, platters, etc.). The spectrum of products
also includes antibacterial washbasins and kitchen count-
ertops with smooth, polished or rough surfaces. The use of
slates for roof and fac¸ade-cladding material has not lost its
architectural importance. For this reason standards and
quality criterions have been defined for roof and fac¸ade-
cladding slates in several economic regions (EU, USA,
etc.). The quality criteria defined by these standards are
matched by the traditional slate deposit (e.g., Mosel slate,
Thu¨ringer slate, Spanish slates, English slates), as well as
by some of the new slate deposits (e.g., Chinese slates).
Traditional local use of fissile rocks in the areas of their
exploitation is still common today, e.g., Gneiss in Swit-
zerland and the ‘‘Alta Quartzite’’ in northern Norway.
Since the middle of the twentieth century, slates from
Uruguay have been utilized in the whole country for wall
cladding and floor tiles (Fig. 1e, f).
Geological setting of Uruguayan slates
The Precambrian basement of Uruguay is represented, from
west to east, by the Rı´o de la Plata Craton (Almeida 1971;
Oyhantc¸abal et al. 2011), the Nico Pe´rez Terrane (Bossi and
Ferrando 2001; Oyhantc¸abal et al. 2011), the Dom Feliciano
Belt (Fragoso Ce´sar 1980), the Punta del Este Terrane
(Preciozzi et al. 1999) and the Rocha Group (Fig. 3). The Rı´o
de la Plata Craton (RPC) in Uruguay corresponds to the Piedra
Alta Terrane, which includes metavulcanosedimentary belts
and a central granitic-gneissic complex of Paleoproterozoic
age (Bossi and Ferrando 2001; Oyhantc¸abal et al. 2011).
The Nico Pe´rez Terrane (NPT), which was originally
defined as part of the RPC (Bossi and Campal 1992), was
recently excluded from the craton by Oyhantc¸abal et al.
(2011) on the basis of differences in the tectono-strati-
graphic evolution of both units. The NPT is bounded to the
west by the RPC through the Sarandı´ del Yı´ Shear Zone
(SYSZ) and to the east and southeast by the Dom Feliciano
Belt (DFB) (Fig. 3).
The DFB is the result of the collision of the Rı´o de la
Plata, Congo and Kalahari cratons that took place during
the Late Neoproterozoic (Brasiliano Cycle) (Porada 1989).
This collision led to the amalgamation of West Gondwana
(Brito Neves and Cordani 1991). The DFB comprises a
granite, schist and foreland belt that extends from south-
ernmost Uruguay to southern Brazil (Rio Grande do Sul
and Santa Catarina states) (Basei et al. 2000). The Lava-
lleja Group (Bossi et al. 1965; Sa´nchez Bettucci 1998)
represents the schist belt in Uruguay (Basei et al. 2008).
Especially relevant for the present work is the Lavalleja
Group (LG), since here are located the dolomitic slate
deposits. This unit was first defined by Bossi et al. (1965),
being further studied by Midot (1984), Sa´nchez Bettucci
(1998), Sa´nchez Bettucci and Ramos (1999) and
Oyhantc¸abal et al. (2001). All these authors agree that the
LG is composed of metavolcanic and metasedimentary
sequences that underwent metamorphism under greenschist
to lower amphibolite facies conditions. This group crops
out to the north of Pan de Azu´car city to 70 km northwest
of Treinta y Tres city, and between SYSZ and Sierra de
A´nimas Complex (to the west) and Carape´ Complex (to the
east) (Fig. 3).
In the southern region the LG was further subdivided by
Midot (1984), Sa´nchez Bettucci (1998) and Oyhantc¸abal
et al. (2001). The first author defines the Minas and Fuente
del Puma Series, while the second author, recategorized
these units as formations and added a third one: the Zanja
del Tigre Formation. Oyhantc¸abal et al. (2001) proposed a
different approach, subdividing the LG into four litholog-
ical associations. These associations are, from west to east:
La Plata (LPA), Pen˜a Blanca (PBA), Minas Viejas (MVA)
and Zanja del Tigre-Cuchilla Alvariza (ZTCAA).
The lithologies of the current investigation belong to the
Fuente del Puma Formation (Midot 1984; Sa´nchez Bettucci
1998) or to the lithological association Minas Viejas
(Oyhantc¸abal et al. 2001). The preferred classification used
in this study is the one defined by Oyhantc¸abal et al.
(2001), since it presents a more detailed analysis in the
considered area. The MVA is where the dolomitic slate
deposits are exposed. The northwestern boundary of this
association with the PBA is the Pen˜a Blanca Lineament,
which also acts as a boundary with the LPA to the south.
The Mina Oriental Lineament is the boundary of the
MVA with the ZTCAA (to the east) and with the Carape´
Fig. 2 Export of processed slate from the main producing countries
between 1995 and 2007 (data after Montani 2008)
1364 Environ Earth Sci (2013) 69:1361–1395
123
Granitic-Gneissic Complex, the syn-tectonic Brasiliano
granites and a pre-Brasiliano basement (to the north).
The MVA, as originally defined, is composed of cal-
careous phyllites, basic metavolcanics, limestones, and
metapelites. Geomorphologically, this association forms
NNE elongated hills in the south central region, with very
steep slopes and associated V-shaped valleys. While in the
north the hills show less pronounced slopes and the valleys
are narrow and flat bottom-shaped (Oyhantc¸abal et al.
2001). These authors considered that the calcareous phyl-
lites are the predominant lithological type. They form
outcrops of elongated ridges kilometers in scale and always
in the upper topographic positions. An excellent layering
defines these exposures, determined by alternating car-
bonate and phyllosilicate layers and a well-developed
cleavage.
These structural features correspond to a regional
transpressional tectonic regime and are defined by strike–
slip faults, thrust faults and megafolds observable in aerial
and satellite images. Further details to the structural fea-
tures observed in the studied lithologies are described in
the deposit characterization subchapter.
Lithological inventory
The main slate quarries active in Uruguay today were
sampled for geochemical and petrographic analysis. In
order to identify the factors leading to a commercially
viable stone, other locations were sampled where mining
was unsuccessful. Several internationally known slates
were also analyzed as a reference for comparison (e.g., the
Fig. 3 Geological map of
southeastern Uruguay. The
location of the dolomitic slates
mining district is indicated
(redrawn after Oyhantc¸abal
et al. 2010 and Sa´nchez Bettucci
et al. 2010)
Environ Earth Sci (2013) 69:1361–1395 1365
123
Spanish roofing slates). All the rocks investigated are listed
in Table 1 with their corresponding lithology, location and
sample abbreviation.
Geochemistry
The geochemistry of the slates was determined by X-ray
fluorescence (XRF). The results are given in Tables 10, 11
(Appendix). The major components of the slates are SiO2,
Al2O3, Fe2O3t, MgO, CaO, Na2O, K2O and CO2.
The SiO2 content varies from 29.15 wt% in the red-
green variety (UY-21) to 66.9 wt% in Vila Nova de Foz
Coˆa (PO). The Uruguayan varieties that show higher con-
tents of SiO2 are Piedra laja rosada con gris (UY-106) and
Piedra laja Puntas del Chafalote (UY-108), with 56.27 and
60.92 wt%, respectively.
Al2O3 shows a similar distribution, although is present
in a lower proportion: between 6.07 wt% in Piedra laja
verde oscura (U38C) and 24.49 wt% in Ardo´sia de Can-
elas (PL). The proportion of Al2O3 is higher for the
Uruguayan varieties UY-106 and UY-108 than the other 15
Uruguayan samples. The highest Al2O3 values were ana-
lyzed for the samples of other countries (e.g., Argentina,
Spain; Table 10).
The Fe2O3t content shows a similar trend, varying from
1.90 wt% in Piedra laja verde clara (U38D) to 10.21 wt%
in Ardo´sia de Canelas (PL). In the Uruguayan varieties the
higher values of Fe2O3t are found in UY-106 and UY-108,
with 6.52 and 4.78 wt%, respectively. Note that all the Fe
present is shown as Fe2O3t, not discriminated from FeO.
The MgO, CaO and CO2 contents show a clear rela-
tionship, so that the samples with higher contents of MgO
and CaO also show the higher content of CO2. This is due
to the fact that these three oxides combine with CO2 to
form carbonates. Ardo´sia Gaspar (GA) shows the lowest
CO2 content. The highest contents of MgO are observed in
the variety Piedra laja gris plomo (UY-19) with
12.84 wt%, and in general, for all Uruguayan slates ana-
lyzed with the exception of UY-108.
Another negative correlation is observed between the
carbonate-forming oxides and SiO2 as well as Al2O3. Na2O
Table 1 List of investigated slates
Trade name Sample Lithology Company/location
Piedra laja negra U33 Slaty dolomitic semipelite Caorsi Hnos, Arroyo Mataojo, Lavalleja
Piedra laja negra U45 Slaty dolomitic semipelite Rufo Hnos, Arroyo Mataojo, Lavalleja
Piedra laja ocre U38A Slaty dolomitic semipelite Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja gris plomo U38B Slaty dolomitic semipelite Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja verde oscura U38C Slaty dolomitic metacarbonate rock Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja verde clara U38D Slaty dolomitic metacarbonate rock Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja verde clara ‘‘macho’’ U38M Slaty dolomitic metacarbonate rock Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja gris plomo UY-19 Slaty dolomitic metacarbonate rock Francesco Carinci, Arroyo Minas Viejas, Lavalleja
Piedra laja ocre UY-21 Slaty dolomitic metacarbonate rock Francesco Carinci, Arroyo Minas Viejas, Lavalleja
Green carbonatic slate with S2 UY-45 Slaty dolomitic semipelite Francesco Carinci, Arroyo Minas Viejas, Lavalleja
Piedra laja ocre UY-54 Slaty dolomitic semipelite Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja gris y negra UY-85 Slaty dolomitic psammite Arroyo Mataojo, south of Rute 81, Maldonado
Green carbonatic folded slate UY-87 Slaty dolomitic metacarbonate rock Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Green carbonatic slate with S2 UY-88 Slaty dolomitic semipelite Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja verde oscura UY-90 Slaty dolomitic metacarbonate rock Carmine Rufo, Arroyo Minas Viejas, Lavalleja
Piedra laja rosada con gris UY-106 Slaty dolomitic pelite Rufo Hnos, Road School 90, Lavalleja
Piedra laja Rocha UY-108 Slaty muscovitic pelite Puntas del Chafalote, Rocha
Ardo´sia Apiu´na AP Slaty muscovitic pelite Apiu´na, Santa Catarina, Brazil
Ardo´sia Gaspar GA Slaty muscovitic pelite Gaspar, Santa Catarina, Brazil
Piedra Laja San Luı´s AR Slaty muscovitic pelite El Trapiche, San Luı´s, Argentina
Ardo´sia de Canelas PL Slaty muscovitic pelite Arouca, Aveiro, Portugal
Sauerland Schiefer WS Slaty muscovitic pelite Sauerland, Germany
Pizarra de techar 120 Slaty muscovitic pelite La Fraguin˜a, Carballeda de Valdeorras, Galicia, Spain
Pizarra de techar 150 Slaty muscovitic pelite Valdemiguel, Carballeda de Valdeorras, Galicia, Spain
Xisto negro de Foz Coˆa PO Slaty muscovitic semipelite Vila Nova de Foz Coˆa, Guarda, Portugal
Lotharheil Schiefer LO Slaty muscovitic semipelite Lotharheil, Geroldsgru¨n, Germany
Theuma Fruchtschiefer TH Slaty muscovitic pelite Vogtland, Sachsen, Germany
1366 Environ Earth Sci (2013) 69:1361–1395
123
varies from less than 0.01 wt% in almost all Uruguayan
slates to 2.52 wt% in Xisto negro de Foz Coˆa (PO). K2O
values range from 1.83 wt% in Piedra laja verde clara y
oscura ‘‘macho’’ (UY-19) to 4.64 wt% in UY-108.
Organic carbon
Knowing the organic carbon content is essential when
relating it with some of the rock properties, such as the
color and the antibacterial properties. The total carbon
(Ctot) in the analyzed slates varies from 0.00 wt% in the
Theuma Fruchtschiefer (TH) (Fischer et al. 2011) to
7.34 wt% in the Piedra laja verde clara (U38D) (Table 2).
Dolomitic slates show a higher proportion of Ctot in all the
samples analyzed, with the proportion varying between
3.40 wt% in Piedra laja negra Rufo Hnos (U45) and
7.34 wt% in the already mentioned U38D. The pelitic and
semipelitic slates contain Ctot values up to 0.87 wt%, as in
the case of Ardo´sia Apiu´na (AP).
Considering how much of the carbon present is actually
organic carbon is important because of the antimicrobial
properties of the organic compounds, especially of the
sulfonated shale oils (Listemann et al. 1993; Fluhr et al.
1998; Gayko et al. 2000). Organic carbon (Corg) contents
are very low in all the samples analyzed; between
0.00 wt% in TH (Fischer et al. 2011) and 0.51 wt% in the
Sauerland Schiefer (WS). The Corg content in the dolomitic
slates ranges from 0.10 to 0.18 wt% and represents
between 1.6 and 3.8 % of the Ctot present.
Pelitic and semipelitic slates show a Corg content
between 0.11 and 0.51 wt% of the whole sample, being
markedly higher for some samples in comparison to the
dolomitic slate group. The proportion of Corg in the Ctot is
very high and ranges between 18.8 and 95.5 wt% in the
pelitic and semipelitic slates (Table 2).
Petrography
The petrography of the investigated slates show a wide
variation (in mineralogy, fabric, etc.), especially when
comparing the dolomitic slates to the pelitic and semipe-
litic slates. The main difference is the occurrence of car-
bonate minerals, which are present in very high proportions
in the first group, and are practically absent in the other two
groups.
Determining mineral compositions in fine-grained me-
tasedimentary rocks is often difficult by conventional
optical microscopy, and thus alternative approaches were
applied. The software Slatenorm (Prof. Dr. Dieter Jung,
p.c.) and the X-ray diffraction Rietveld method were used
to quantify the mineralogical composition (Tables 3, 12).
The first method calculates the normative minerals using
the geochemistry, while the second performs a quantitative
phase analysis using the XRD results. A strong correlation
exists between both methods on the amounts of quartz.
However, in the case of the phyllosilicates the correlation
is not so obvious because of the uncertainty concerning
the composition of these minerals (Ward and Go´mez
Table 2 Total carbon (Ctot), total organic carbon (Corg), total carbonatic carbon (Ccarb), total nitrogen (Ntot) and total sulfur (Stot)
Sample Ctot Corg Ccarb CaCO3 Ntot Stot Corg/N Corg/S
U33 4.66 0.18 4.48 37.3 0.020 0.116 9.0 1.6
U45 3.40 0.12 3.28 27.3 0.017 0.022 7.1 5.5
U38A 6.18 0.10 6.08 50.7 0.011 0.003 9.1 33.3
U38B 4.99 0.11 4.88 40.7 0.012 0.002 9.2 55.0
U38C 7.29 0.12 7.17 59.7 0.013 0.003 9.2 40.0
U38D 7.34 0.12 7.22 60.2 0.013 0.022 9.2 5.5
U38M 6.97 0.11 6.86 57.2 0.013 0.098 8.5 1.1
AP 0.87 0.16 0.71 5.9 0.034 0.006 4.7 26.7
GA 0.14 0.13 0.01 0.1 0.042 0.006 3.1 21.7
AR 0.12 0.11 0.01 0.1 0.019 0.070 5.8 1.6
PL 0.40 0.39 0.01 0.1 0.079 0.233 4.9 1.7
WS 0.74 0.51 0.23 1.9 0.083 0.300 6.1 1.7
120 0.41 0.38 0.03 0.2 0.053 0.070 7.2 5.4
150 0.44 0.42 0.02 0.2 0.057 0.076 7.4 5.5
PO 0.21 0.20 0.01 0.1 0.035 0.111 5.7 1.8
LO 0.80 0.15 0.65 5.4 0.032 0.043 4.7 3.5
TH 0.00* 0.00* 0.00* 0.0* n.d. 0.0* n.d. 0.0*
* Data after Fischer et al. (2011)
Environ Earth Sci (2013) 69:1361–1395 1367
123
Ferna´ndez 2003). In the dolomitic slates, the values for
these phyllosilicates obtained by both methods are similar
when illite coexists with muscovite. However, for the rest
of the slates studied such a simple correlation does not
exist; the chlorite contents are higher using the Rietveld
method. Dolomite contents are similar when using both
methods.
The normative mineralogical composition obtained has
been used to classify the slates with respect to the
nomenclature of the British Geological Survey (Robertson
1999). Following this classification schema, three different
categories are used based on the quartz, feldspar, phyllos-
ilicate and carbonate mineral contents.
The first category is for rocks containing mostly quartz,
feldspar and mica. A second category is for rocks that have
between 10 and 50 % carbonate and/or calc-silicate min-
erals and at least 50 % quartz ? feldspar ? mica. A third
category uses another ternary diagram for the classification
of rocks containing more than 50 % calc-silicate and/or
carbonate minerals (see Fig. 4). Textural and mineralogical
qualifiers (e.g., slaty, dolomitic) are used to present more
information on the classification of these rocks (see Rob-
ertson 1999). For all the rocks studied, the qualifier ‘‘slaty’’
will be used because all of them show a slaty cleavage that
determines their strong fissility.
Uruguay has a relatively large variety of slates, which
are incorrectly described as quartzites (Comunita` Econo-
mica Europea-Uruguay, no date) or chloritic phyllites
(Coronel et al. 1987). Most of the Uruguayan rocks ana-
lyzed contain dolomite as the main carbonate mineral, and
the qualifier ‘‘dolomitic’’ is used instead of the word
‘‘calcareous’’.
The investigated slates (Table 1) were classified into
five subgroups using the schema of Robertson (1999) and
their normative mineralogy (Table 12 in Appendix and
Fig. 4). These groups are: (1) slaty semipelites, e.g., Xisto
negro de Foz Coˆa (PO) and Lotharheil Schiefer (LO)
(Fig. 4a); (2) slaty pelites, includes the majority of the
investigated rocks, as well as the Piedra laja Puntas del
Chafalote (UY-108) (Fig. 4a); (3) slaty dolomitic meta-
carbonate rocks, comprising the following commercial
varieties: Piedra laja verde oscura (U38C), Piedra laja
verde clara (U38D) and Piedra laja verde clara ‘‘macho’’
(U38M) (Fig. 4b); (4) slaty dolomitic semipelites, e.g.,
Piedra laja ocre (U38A), Piedra laja negra Caorsi Hnos
(U33) and Piedra laja gris y negra (UY-85) (Fig. 4b). Note
that the last variety occurs at the border between the cal-
careous semipelites and calcareous psammite, due to its
higher content of quartz and feldspar; and finally (5) the
slaty dolomitic pelites, composed of only one variety,
Piedra laja rosada con gris (UY-106) (Fig. 4b).
For simplicity the five subgroups mentioned above will
be categorized into three main groups. Dolomitic slates are
those rocks that classify as slaty dolomitic metacarbonate
rocks, slaty dolomitic semipelite or slaty dolomitic pelite;
as pelitic slates, rocks that group as slaty pelites; and as
semipelitic slates are those designated as slaty semipelite.
Dolomitic slates
The dolomitic slates are composed mainly of dolomite,
quartz and phyllosilicates (muscovite, illite and chlorite)
(Table 12; Figs. 4b, 5). The normative amount of dolomite
varies between 11.86 wt% in the Piedra laja rosada y gris
(UY-106) and 57.92 wt% in the Piedra laja verde clara
(UY-90). The grain size ranges from 0.04 to 0.18 mm.
Grains are generally anhedral and very difficult to discern
as individual grains (Fig. 5). The black slates show a lower
normative dolomite content, between 23.39 and
32.97 wt%. Calcite is present in a low normative propor-
tion, ranging from 0 to 4.12 wt%, and normative siderite is
present in only two samples at very small amounts,
between 0.08 and 0.16 wt%.
Quartz is the second most important mineral, as its
normative abundance comprises between 19.64 wt% in the
Piedra laja ocre (U38A) and 36.01 wt% in the Piedra laja
rosada con gris (UY-106). It occurs as anhedral grains with
sizes that generally range from 0.05 to 0.12 mm. In the
black slates grain sizes can reach up to 0.30 mm, and
sometimes up to 1.10 mm as in some psammitic layers of
the Piedra laja negra Caorsi Hnos (U33) (Fig. 5a). The
Table 3 X-ray diffraction result for the Uruguayan dolomitic slates
Sample Dolomite Calcite Quartz Albite Muscovite Illite Chlorite Pyrite Rutile Hematite
U33 36.5 0.9 28.4 11.4 15.6 6.7 0.5
U45 24.5 32.9 8.4 24.6 9.6
U38A 49.2 26.6 11.2 11.0 2.1
U38B 40.3 29.9 13.4 12.1 3.2 0.2 0.3 0.6
U38C 55.8 21.9 13.7 2.4 6.0 0.3
U38D 58.5 21.8 10.4 5.9 3.3 0.2
U38M 55.8 22.9 7.1 9.4 4.6 0.3
1368 Environ Earth Sci (2013) 69:1361–1395
123
quartz grains are normally elongated parallel to the folia-
tion with an aspect ratio between 1.5 and 4. In the black
variety of Rufo Hnos (U45) thin layers of about one cen-
timeter, containing up to 50 % medium-grained (0.30 mm)
quartz grains, have been recognized (Fig. 5b). Quartz
sometimes appears recrystallized or with undulose
extinction.
Phyllosilicates form the third most important mineral
component in these rocks. In thin section determining
which phyllosilicate is present is difficult due to the very
fine grain size. The most recognizable is muscovite. This
mineral is one of the main normative phyllosilicates cal-
culated using the program Slatenorm, as it comprises
between 14.59 wt% in the Piedra laja negra con gris (UY-
85) and 31.82 wt% in the Piedra laja rosada con gris (UY-
106).
However, in the majority of the dolomitic slates, the
normative muscovite content is not higher than 24.07 wt%
(Piedra laja negra, Caorsi Hnos). Muscovite appears as
subhedral crystals of around 30–150 lm in size with an
aspect ratio of 4–12. Normative paragonite, a sodium-rich
mica, is only present in the Piedra laja negra Rufo Hnos
and when these two micas coexist, they represent
24.41 wt% of the rock. Therefore, the black dolomitic
slates contain the greater proportion of mica minerals. Only
some of the dolomitic slates studied show normative
chlorite. This mineral has been recognized in hand speci-
mens due to its typical green color, as well as in thin
Fig. 4 Classification of the
investigated slates based on the
normative composition of their
sedimentary protolith (after
Robertson 1999). a Pelitic and
semipelitic slates and
b dolomitic slates (mica*
includes all the minerals not
considered in the other vertices)
Environ Earth Sci (2013) 69:1361–1395 1369
123
1370 Environ Earth Sci (2013) 69:1361–1395
123
sections (e.g. U38A, Fig. 5c) and in X-ray diffraction
(Table 3). The phyllosilicates occur parallel to the S0–1
foliation and in some varieties also along a second foliation
S2 (Fig. 5d) or to folds developed in a later deformation
phase (Fig. 5h).
In the calculations using Slatenorm (Table 12), the
normative chlorite mineral is defined as daphnite (Fe-Al-
chlorite) and the serpentine group consisting of the min-
erals serpentine (Mg-serpentine), amesite (Mg-Al-serpen-
tine) and greenalite (Fe-serpentine). The serpentine group
minerals were not identified in thin section and are not
present in the X-ray diffractograms, being only present as
normative minerals.
There is an inverse correlation between the normative
amount of dolomite on the one side and the normative
content of quartz ? feldspar and mica on the other. The
Piedra laja verde oscura (U38C) and verde clara (U38D)
have the highest normative dolomite content of the com-
mercial varieties analyzed and the lowest proportion of
normative quartz and muscovite (Table 12; Fig. 4b). On
the other hand, the Piedra laja rosada con gris (UY-106)
shows the highest quartz and muscovite normative pro-
portions and the lowest dolomite normative content.
Accessory minerals determined are feldspar, apatite,
tourmaline, zircon and opaques (magnetite and pyrite). In
the black Rufo Hnos (U45) variety, psammitic layers
containing anhedral grains of plagioclase are recognizable
with sizes similar to those of the quartz grains (30 lm).
The reddish colored varieties (U38A–U38M) show patches
red and orange color (possibly iron hydroxides, Fig. 5c).
The black slates have lower proportions of normative
dolomite when compared to the colored slates and show, in
turn, higher proportions of normative quartz and phyllosili-
cates (muscovite, chlorite and illite). This relationship
between the mineralogical composition and the color is con-
firmed by the variety Piedra laja gris plomo (U38B), which is
the darkest slate of the northern district (AMVD) and shows
the lowest proportions of dolomite in the entire mining district.
Pelitic slates
The pelitic slates are the most heterogeneous of the rocks
investigated (Table 12; Figs. 4, 6). These rocks have a high
proportion of normative phyllosilicates (between 38 and
68 %), mainly muscovite, but also chlorite, chloritoid and
minor biotite (in Ardo´sia Apiu´na, AP). The other main
constituents are quartz and feldspar.
Muscovite appears as euhedral crystals with sizes
ranging between 50 and 100 lm. They have an aspect ratio
of 20 and are oriented parallel to the foliation. In the
psammitic layers of sample AP, muscovite grains show
sizes up to 250 lm with an aspect ratio up to 16. Chlorite is
the dominant phyllosilicate in the Piedra laja San Luı´s
(AR). Chlorite is observable in the varieties Pizarra de
techar La Fraguin˜a (sample 120) and Valdemiguel (sample
150), where they appear as mica fishes ranging from 60 to
100 lm in size with an aspect ratio up to two (Fig. 6f).
This observation has also been reported by Ruiz Garcı´a
(1977) and Garcı´a-Guinea et al. (1998).
Chloritoid is present in the Ardo´sia de Canelas (PL) as
euhedral crystals with a size range of 50–100 lm and an
aspect ratio of 10. Their long axes are parallel, transverse
or perpendicular to the foliation (Fig. 6h).
Another important constituent is quartz with a smaller
variation of its proportion, the normative content ranges
between 28 and 34 wt%. This mineral forms anhedral
grains with sizes ranging between 40 and 80 lm, and up to
300 lm in size in the Ardo´sia de Canelas (PL) or 600 lm
in the psammitic layers of the Ardo´sia Apiu´na (AP)
(Fig. 6a). Commonly, in the more phyllosilicate-rich slates
the grains are elongated parallel to the foliation with an
aspect ratio up to six (e.g., Pizarra de techar La Fraguin˜a)
(Fig. 6e, f). In the other varieties, those with lower phyl-
losilicate contents, the grains are very well rounded.
Undulose extinction was not observed.
The other main constituent is feldspar, whose normative
amount varies between 0 and 20.3 wt%. Due to the very
fine grain size, determination with the petrographic
microscope was not possible, with the exception of the
feldspars in the psammitic layers of the Ardo´sia Apiu´na
(AP). The accessory minerals consist of rutile, apatite,
magnetite and pyrite. In the Sauerland Schiefer (WS)
carbonate is also observable as an accessory mineral.
Varieties with a higher content of normative phyllosil-
icates (and lower feldspar) are Arouca (PL), La Fraguin˜a
(sample 120), Valdemiguel (sample 150), Theuma Fruc-
htschiefer (TH) and Sauerland (WS). The high amount of
Corg in the form of graphite ranges between 0.39
and 0.53 wt% (Table 2), and is responsible for their char-
acteristic black or dark gray color. An exception to this
characteristic is sample TH, which shows no presence of Corg
Fig. 5 Thin section images of the investigated samples. The slaty
foliation is parallel to the image length. a Black dolomitic slate (U33)
in cross-polarized light (CPL) with a large quartz clast visible in the
upper left corner. b Piedra laja negra Rufo Hnos (U45) in CPL
containing a distinct psammitic layer. c Piedra laja ocre (U38A) in
plane polarized light (PPL), the phyllosilicatic layer in the center
shows a light green coloration due to chlorite. Note the iron
hydroxide staining above. d Piedra laja gris plomo (U38B) in CPL.
S0–1 and a S2 are indicated by the phyllosillicates. e Piedra laja verde
oscura (U38C) in PPL showing a poor development of phyllosilicatic
layers. f Piedra laja verde clara (U38D) in PPL, phyllosilicate layers
are missing. g Piedra laja verde clara ‘‘macho’’ (U38M) in PPL.
Relatively coarse dolomite, quartz and opaque grains are visible.
h Sample UY-87 in PPL is a green dolomitic slate which shows a
folded S0–1
b
Environ Earth Sci (2013) 69:1361–1395 1371
123
1372 Environ Earth Sci (2013) 69:1361–1395
123
and whose dark gray color is dotted by millimeter-sized
chlorite pseudomorphs after cordierite (Fischer et al. 2011).
Slaty pelites with lower amounts of normative phyllo-
silicates are, in decreasing order: Piedra laja San Luı´s
(AR), Ardo´sia Gaspar (GA), Ardo´sia Apiu´na (AP) and
Piedra laja Puntas del Chafalote (UY-108). Higher pro-
portions of normative serpentine minerals occur with
respect to the other phyllosilicates. These rocks show green
colors, due to the relatively high proportion of modal
chlorite.
Semipelitic slates
Semipelitic slates are rocks with even lower normative
phyllosilicate contents (Fig. 6). Their main constituent is
quartz, whose normative abundance ranges between 33 and
50 wt%, and occurs as anhedral rounded grains of up to
120 lm. In the Xisto negro de Foz Coa (PO) two families
of grain sizes can be differentiated, the smaller group
ranges 40–50 lm and the larger 80–100 lm (Fig. 6g).
Feldspar, with 14–34 wt% normative abundance, is
mainly represented by plagioclase grains showing a similar
grain size to quartz (40 and 100 lm). The normative
phyllosilicates comprise 28–30 wt%, and consist of
muscovite, biotite and chlorite. Muscovite appears as
euhedral crystals 150 lm in size and has an aspect ratio up
to 15. Biotite is subhedral to anhedral and finer in sample
PO (up to 30 lm in size with an aspect ratio of around
one). In the Lotharheil Schiefer (LO) biotite is subhedral,
shows a grain size up to 100 lm and an aspect ratio of
around three. Euhedral hexagonally shaped crystals of
chlorite are less frequent and around 30 lm in size.
Calcite appears as anhedral crystals generally 80 lm in
size. Sometimes it exhibits a poikiloblastic texture in the
LO (patchy-shaped grains) ranging in size between 150
and 300 lm, partially surrounding grains of quartz and
muscovite. The normative abundance is higher in the LO
(5.5 wt%). Very coarse calcite crystals are also found
occurring as veins in the PO (e.g., one calcite vein is
2.8 mm in length and 0.16 mm wide).
Accessory minerals include euhedral apatite and zircon,
and anhedral to subhedral magnetite and pyrite. They are
disseminated throughout the rock and show very fine grain
sizes up to 20 lm.
Opaque minerals
The opaque minerals present in all the slates include
magnetite, chalcopyrite and pyrite. Their shapes, propor-
tion and distribution vary widely from slate to slate.
In the dolomitic slates the opaques mainly consist of
magnetite and pyrite. Magnetite appears in almost all
samples as 5–20 lm anhedral to euhedral crystals, nor-
mally disseminated in the rock. Pyrite usually appears as
5–20 lm anhedral crystals. In some of the samples, rela-
tively coarser (350–500 lm) euhedral crystals are present,
in veins or in the foliation surface, especially in the black
varieties (U33, U45 and UY-85) and in a non-fissile variety
(U38M) (Fig. 5g). Chalcopyrite is present in two of the
samples as euhedral crystals 5–20 lm in size.
Magnetite and pyrite are also the main opaque constit-
uents of the pelitic slates. These two minerals are present as
very fine-grained disseminated crystals (around 20 lm).
Pyrite tends to be euhedral and magnetite subhedral to
anhedral. However, in the variety Ardo´sia de Canelas (PL)
the fine-grained pyrite crystals (20 lm) occur in lenses of
up to 2.6 mm in length and 1.0 mm in width.
In the Piedra laja San Luı´s (AR), subhedral magnetite is
the dominant opaque mineral and shows two distinct grain
sizes. The finer grained crystals are about 20 lm in size
and the coarser grains are up to 110 lm. Pyrite crystals are
subhedral and tend to be elongated, having a size up to
130 lm with an aspect ratio of four. Their proportion in
these rocks is relatively higher than for the other rocks
analyzed.
Magnetite and pyrite also appear as anhedral to subhe-
dral grains in the semipelitic slates. They have very fine
grain sizes (up to 20 lm) and are evenly disseminated
throughout the rocks. Pyrite is also found in veins, around
60 lm thick and 15 cm length. Together with magnetite
pyrite is also found along solution transfer surfaces.
Rock fabric
The rock fabric together with the mineral composition
controls the physical and mechanical properties and the
de´cor of a dimensional stone, which holds true especially
Fig. 6 Thin section images of the investigated slates. The slaty
foliation is parallel to the image length. a Ardo´sia Apiu´na (AP) in
CPL with quartz grains showing undulatory extinction in the
psammitic layers. b Piedra laja San Luı´s (AR) in PPL. Quartz vein
crosscuts the foliation as determined by the alignment of chlorite.
c Ardo´sia de Canelas (PL) in CPL. Quartz microlithons between
phyllosilicatic layers and a lens of tiny pyrite porphyroblasts.
d Ardo´sia de Canelas (PL) in PPL. Note the chloritoid porphyroblast
surrounded by or transversal to the foliation. e Pizarra de techar La
Fraguin˜a (120) in CPL with a very well-developed foliation. Quartz
and chloritoid grains are elongated parallel to the foliation. f Detail of
the texture in the Pizarra de techar La Fraguin˜a (120) in PPL. Note the
chlorite ‘‘fish’’ in the center with a light green color and the white
quartz grains. g Xisto negro de Foz Coˆa (PO) in PPL with opaques
and a phyllosilicate-rich, irregular solution transfer foliation. Note the
lighter and darker domains, the latter with a relatively higher
proportion of phyllosilicates and a finer grain size. h Detail of the
solution transfer foliation in the Xisto negro de Foz Coˆa (PO) in PPL
b
Environ Earth Sci (2013) 69:1361–1395 1373
123
in the case of the slates. As illustrated in Fig. 7, four main
rock fabric types have been determined for the slates ana-
lyzed. The presence of a spaced foliation is a characteristic
feature common in the majority of the fabric types. This
foliation is defined by cleavage domains that are essentially
composed of orientated phyllosilicates and microlithons
consisting of an ensemble of minerals that are in between
these cleavage domains (Passchier and Trouw 1996).
According to Shelley (1993), the cleavage domains are M or
P domains (for mica- or phyllosilicate-rich domains) and
the microlithons are the Q domains (quartz-rich domains).
In the dolomitic slates the microlithons have, in addition to
quartz, also a high proportion of dolomite.
1. Fabric type I The cleavage domains are practically
absent or poorly developed due to the very low grade
metamorphic conditions that the rock underwent. The
rock splits parallel to the bedding plane, especially
along bedding planes that are characterized by signif-
icant differences in grain sizes. These are the so-called
parallel slates. The individual grains do not show any
preferred orientation and are equidimensional. The
slate Ardo´sia Gaspar (GA) is a good example for this
fabric type (Fig. 7a). This sample shows layers that are
more fine-grained, with a poorly developed S1
foliation, which determines an intersection lineation
(L1) with the foliation S0.
2. Fabric type II is characterized by the abundance of
cleavage domains determining a very well-developed
slaty cleavage, being the plane along which the rock
splits. Individual quartz and chlorite grains of the
microlithons are deformed, generally showing oblate
to prolate shapes. A stretching lineation is defined by
the grains that are oriented with their long axis parallel
to the foliation plane. A typical example is the Spanish
slate Pizarra de techar La Fraguin˜a (sample 120),
whose fabric is illustrated schematically in Fig. 7b. A
special case of this fabric type is the slate Ardo´sia de
Canelas (PL), where the long axes of chloritoid
porphyroblasts are perpendicular, transversal or paral-
lel to the foliation and also millimeter-thick lenses
composed of tiny pyrite porphyroblasts occur. The
chloritoids of Ardo´sia de Canelas are wrapped by the
last foliation Sn?1, therefore they are pre-deformation
phase Dn?1. They are post-tectonic to the foliation
developed in deformation phase Dn, since they are not
completely aligned.
3. Fabric type III A wider range of fabric types is
summarized in this group. This group shows more than
one foliation and the angle between the planar fabrics
Fig. 7 Rock fabrics (see
explanation in the text)
1374 Environ Earth Sci (2013) 69:1361–1395
123
may differ. The main foliation, which can be described
as a slaty cleavage, is generally parallel to the original
bedding plane of the protolith due to transposition, e.g.,
in the slate Laja Negra Rufo Hnos (U45) and it is
defined as S0–1. In most of the cases another foliation
occurs (S2), as some of the phyllosilicate flakes were
reoriented in response to a later folding event. Conse-
quently, this kind of fabric also contains a lineation as
the result of the intersection of these two foliations (L2).
If both foliations have a relatively small angle between
each other (e.g., 8 in sample UY-45) scales or flakes
that easily break will develop. In cases where the angle
between both foliations is larger (e.g., 15 in sample
U38B or 23 in U38A), the main foliation shows
undulations on the order of microns. In Fig. 7c this
fabric is illustrated for the Uruguayan dolomitic slates.
For commercial use the S0–1 should be the dominant
foliation because it controls the mechanical behavior.
Additionally, the angle between both foliations should
not be larger than 30, because then the rock does not
split easily parallel to S0–1 and the surface obtained will
not be smooth (e.g., development of steps).
4. Fabric type IV It is mainly characterized by the lack of
flatness of the foliation surface. The most complex
example is illustrated by the Xisto negro de Foz Coˆa
(PO), which shows a foliation characterized by
pressure solution and solution transfer processes and
two domains with different grain sizes. The cleavage
domains are composed of pyrite, muscovite and biotite
and their thickness varies between 8 and 65 lm. The
microlithons comprise very fine-grained domains
(quartz grains \ 63 lm) and coarser grained domains
(quartz up to 80 lm). The coarser grained domains are
prolate, 1–5 mm in diameter and 1–10 cm in length.
Their long axes define a lineation parallel to the
foliation plane very often surrounded by the solution
transfer foliation. Another, less well-developed folia-
tion can be observed perpendicular to the main
foliation, which is characterized by pelitic domains.
Additionally, carbonate, quartz and pyrite veins cross-
cut the rock in all directions. As for the Lotharheil
Schiefer (LO), this kind of fabric is responsible for a
very rough foliation surface (Fig. 7d).
Mica layers and mass value
The mass value is a very important parameter to be taken
into account when evaluating the suitability of a slate for
commercial use, as it controls its fissility. This parameter
was developed by Bentz and Martini (1968) and later
included in the DIN EN 12326-2 (2000).
No clear knowledge exists of how exactly the mica
layers influence the flexural strength and workability of the
slates. The modality for measuring the mica layers is
described in European technical norm for roofing slates
(DIN EN 12326-2 2000); however, this parameter should
be taken as an approximation. Variations of 10–15 mica
layers per mm can occur depending on the person mea-
suring and the procedure used (e.g., measurement with the
microscope or using a printed image). Wagner (2007)
calculated the mass value for several slates. This parameter
is the product of the number of mica layers per mm by the
average width of the mica layers multiplied by ten.
The values obtained for the studied slates varies from
0.12 to 8.12, and although these values are lower when
compared with those obtained by Wagner (2007), a general
trend can be observed (Table 4; Fig. 8). The dolomitic
slates show lower mass values. They represent a lower
number of mica layers per millimeter, between 7.5 and
39.7, and similar mica layer widths as the pelitic slates,
with the exception of the Piedra laja ocre (U38A) that
shows a mica layer width of 0.106 mm.
The phyllosilicate-rich pelitic slates show a very high
mica layer per millimeter, between 40.5 (Ardo´sia de
Canelas) and 123.7 (Pizarra de techar La Fraguin˜a).
Although the Ardo´sia Gaspar and Ardo´sia Apiu´na are pe-
litic slates, they have with a very low mica layer number
per millimeter of 1.2 and 2.5, respectively.
The semipelitic slates show the lowest mass values as
they represent extremely low values of mica layers per
millimeter, between 0.5 and 0.7. Wagner (2007) observed
Table 4 Width of mica layers, mica layers per mm and mass value
calculated for the samples analyzed
Sample Width of mica
layers (mm)
Mica layers/mm Mass value
U33 0.007 39.7 2.96
U45 0.003 16.9 0.51
U38A 0.106 9.7 10.28
U38B 0.010 25.5 2.56
U38C 0.008 11.0 0.87
U38D 0.013 7.5 0.98
U38M 0.007 20.4 1.38
AP 0.010 2.5 0.25
GA 0.010 1.2 0.12
AR 0.007 108.4 7.22
PL 0.020 40.5 8.12
WS 0.011 55.8 5.99
120 0.004 123.7 5.50
150 0.009 62.8 5.57
PO 0.042 0.7 0.28
LO 0.032 0.5 0.16
Environ Earth Sci (2013) 69:1361–1395 1375
123
that the slates with a number of mica layers per millimeter
lower than 40 are not suitable as roofing and fac¸ade slates.
The analyzed slates that have a higher number of mica
layers per millimeter than 40 are the Spanish roofing slates
(samples 120 and 150), Piedra Laja San Luis (AR), Sau-
erland Schiefer (SW) and Ardo´sia de Canelas (PL).
Physical and mechanical rock properties
The application of a slate is fundamentally determined by
its physical and mechanical properties. The relevant
properties are flexural strength, relative water uptake,
temperature cycling tests, and stability during freezing,
color, acid, leaching and heat. According to Wagner
(2007), a low flexural strength is associated with a high
water uptake. At a water uptake of about \0.4 wt% a
flexural strength of 50–70 MPa is expected (see discussion
in Wagner 2007). Also a high water uptake can be related
to the weathering of ore and carbonate minerals.
Bulk density, matrix density, porosity
The mechanical instability or mechanical deterioration of
the rock fabric, for example through frost damage or other
climatic influences, is related to a high porosity, therefore a
low density, but also to a high water uptake. For the
application as roofing or fac¸ade cladding a comparable
high flexural strength is required.
The bulk density, the matrix density and the porosity
were measured using the Archimedes method, as described
in Monicard (1980). The bulk density of the investigated
slates ranges from 2.72 to 2.83 g/cm3 (Table 5). The
lowest values are observed for the Ardo´sia Apiu´na (AP)
and Lotharheil Schiefer (LO), while the higher values
belong to the Piedra laja verde oscura (U38C), Piedra laja
verde clara (U38D) and Piedra laja verde clara ‘‘macho’’
(U38M).
The matrix density shows a similar variation, between
2.73 and 2.87 g/cm3 (Table 5) for the Ardo´sia Apiu´na (AP)
and Lotharheil Schiefer (LO), varieties which show the
lowest values. Ardo´sia de Canelas (PL) shows the highest
matrix density corresponding to the high content of Fe2O3t
(10.21 wt%), which is mainly present as magnetite lenses
parallel to the foliation.
The dolomitic slates show relatively high matrix den-
sities, e.g., between 2.78 and 2.84 g/cm3. This is due to the
higher proportion of dolomite in these rocks, a mineral
with a higher density (2.87 g/cm3, Robie and Bethke 1966)
than the main constituents of slates (quartz and the chlorite
group).
The porosity of the slates is normally low, between 0.10
and 2.46 % (Table 5). The lowest value is registered by the
Piedra laja verde oscura (U38D) and the highest is
observed for the Ardo´sia de Canelas (2.46 %). With
respect to the porosity two groups of slates can be distin-
guished: one group, represented by the dolomitic slates has
values lower than 0.30 % corresponding to a higher bulk
density. The second group is represented by slates with
C0.30 % porosity, e.g., quartz- and phyllosilicate-rich
slates.
The values of the bulk density of the slates given in
Table 5 are higher than the 75 % quartile for metamorphic
rocks discussed by Mosch and Siegesmund (2007). Com-
paring the porosity values compiled by these authors, it is
obvious that the dolomitic slates represent the upper
(dolomitic slates) and lower extreme values (pelitic slates),
whereas the pelitic and semipelitic varieties are the upper
outliers.
The average pore radius determined by mercury injec-
tion porosimetry ranges between 0.01 lm for the Piedra
laja negra Rufo Hnos (U45) and 0.31 lm in the Pizarra de
techar Valdemiguel (150). Most pore radii range between
0.05 and 5.31 lm. The lowest values are observed for the
following samples, e.g., Piedra laja negra Rufo Hnos
(U45), Ardo´sia Apiu´na (AP) and Theuma Fruchtschiefer
(TH); while Xisto negro de Foz Coˆa (PO) exhibits the
highest value. According to Klopfer (1985), in micropores
with a pore diameter \0.1 lm, water will condense at
relative humidity (RH) values below 99 %. Capillary
suction is practically relevant to materials for pore diam-
eters between 1 lm and 1 mm, the so-called capillary
pores.
The atmospheric water uptake or absorption determined
following the DIN EN 13775 (2001) is relatively low for
all samples studied covering the range between 0.03 and
0.74 wt% (Table 5). Most of the samples show values
lower than 0.30 wt%. The exceptions are the Theuma
Fig. 8 Diagram of width of mica layers versus mica layers per mm
(modified after Wagner 2007)
1376 Environ Earth Sci (2013) 69:1361–1395
123
Fruchtschiefer (TH) and the Ardo´sia de Canelas (PL) with
values of around 0.40 wt% (Natursteinwerk Theuma AG
2012) and 0.74 wt%, respectively. All the dolomitic slates
show values B0.12 wt%, in contrast to some pelitic and
semipelitic slates (see Table 5).
The values of water uptake of the Uruguayan commer-
cial slates are within the upper and lower quartile of the
values for roofing slates compiled by Wagner (2007). Most
of the slates belonging to the pelitic and semipelitic groups
have values between both quartiles, but some of them (PL
and TH) show values higher than the upper quartile. If the
water uptake is higher than 0.6 wt%, the frost resistance
must be determined using the DIN 52104 for 100 freeze–
thaw cycles.
Antimicrobial properties
For the utilization of slates as countertops and even as
cutting boards is relevant to know their antimicrobial
properties. For this purpose the studied slates were exposed
to two kinds of bacteria: Escherichia coli (E. coli) and
Bacillus subtilis (B. subtilis) and a fungus: Aureobasidium
pullulans (A. pullulans). Their growth after 10 days was
evaluated. Two kind of standard medium were used for the
growing of the bacteria: lysogeny broth (LB) and potato-
dextrose agar (PDA).
The results obtained are listed in Table 6. A lower
growth of E. coli in the LB medium is observed while in
most of the samples no growth is observed. The samples
that show weak growth of this bacterium are Piedra laja
negra Rufo Hnos (U45) and Pizarra de techar Valdemiguel
(150). Ardo´sia Apiu´na (AP) and Piedra laja verde clara
‘‘macho’’ (U38M) show a moderate growth. In PDA
medium a higher growth is observed for some of the
samples considered, especially in Piedra laja verde claro
macho (U38M), Ardo´sia Apiu´na (AP), Xisto negro de Foz
Coˆa (PO) and the control sample Moskart Granite (U7),
which show high growth (confluent growth of colonies).
In the case of B. subtilis a higher growth is observed for
both mediums while for most samples it is moderate to high,
with the exception of Ardo´sia de Canelas (PL) which shows
Table 5 Density, porosity and pore radii distribution in the analyzed samples
Trade name ID Bulk density
(g/cm3)
Matrix density
(g/cm3)
Porosity
(%)
Average pore
radii (lm)
Most frequent pore
radii (lm)
Water uptake
atm. (wt%)
Piedra laja negra,
Caorsi Hnos
U33 2.78 2.78 0.19 0.253 0.531 0.06
Piedra laja negra, Rufo
Hnos
U45 2.80 2.81 0.16 0.010 0.005 0.05
Piedra laja ocre U38A 2.82 2.83 0.23 0.069 0.021 0.12
Piedra laja gris plomo U38B 2.82 2.83 0.17 0.056 0.013 0.07
Piedra laja verde
oscura
U38C 2.83 2.84 0.13 0.073 0.084 0.06
Piedra laja verde clara U38D 2.83 2.83 0.10 0.061 0.005 0.05
Piedra laja verde clara
‘‘macho’’
U38M 2.83 2.83 0.26 0.171 0.021 0.07
Piedra laja Puntas del
Chafalote
UY-
108
2.72 2.74 0.62 n.d. n.d. 0.24
Ardo´sia Apiu´na AP 2.72 2.75 1.05 0.034 0.005 0.24
Ardo´sia Gaspar GA 2.75 2.77 0.59 0.09
Piedra Laja San Luis AR 2.78 2.80 0.80 0.18 0.28
Ardo´sia de Canelas PL 2.80 2.87 2.46 0.74
Sauerland Schiefer WS 2.77 2.79 0.51 0.077 0.008 0.20
Pizarra de techar La
Fraguin˜a
120 2.77 2.80 0.84 0.142 0.005 0.14
Pizarra de techar
Valdemiguel
150 2.78 2.79 0.39 0.310 0.531 0.16
Xisto negro de Foz
Coˆa
PO 2.74 2.75 0.42 0.245 5.309 0.10
Lotharheil Schiefer LO 2.72 2.73 0.30 0.020 0.005 0.03*
Theuma Fruchtschiefer TH 2.74** n.d. 0.95** 0.096? 0.005? 0.40**
* Data after Siegesmund and Stein (2007); ** data after Weiss et al. (2004), ? data after Fischer et al. (2011); ?? data after Natursteinwerk
Theuma AG (2012)
Environ Earth Sci (2013) 69:1361–1395 1377
123
a weak growth. Ardo´sia Apiu´na (AP) shows no growth in
LB medium and a very high growth in PDA medium.
For A. pullulans the number of colonies in 0.25 mm2
gives the information of the antimicrobial property of a
slate. Most of the slates show no growth of colonies, with
the exception of Ardo´sia Apiu´na (AP) and Ardo´sia Gaspar
(GA). The first pelitic slate show 1–2 colonies and GA
show 5, which is the highest value registered for the
samples considered. The control group, composed by
sandstone, granite and marble, presents 0–2 colonies.
Mechanical properties
A coordinate system determined by the foliation and line-
ation observed in the rocks was established. The foliation
determines the xy-plane and the lineation the x-direction.
Flexural strength
The relevance of the flexural strength in any dimensional
stone is because this petrophysical property determines the
resistance to bending stresses, such as those experimented
on with rear-ventilated fac¸ades or stairways (Siegesmund
and Du¨rrast 2011). According to these authors, the dam-
ages produced by the overcoming of these stresses are
more important than those produced by shear or com-
pressive stresses.
The fissility of a natural layer is a positive aspect during
the manufacturing of building elements on one hand; on the
other hand, it is the weakest point of strength in the con-
struction. Therefore, each contribution using fissile
dimensional stones must take into account the flexural
strength. Flexural strength tests have to be performed and
to be compared to the potential flexural forces in the con-
struction. This is of primary importance for the following
construction elements: fac¸ade panels with lateral and back
slide anchors, floor tiles with dynamic shear stress (heavy-
duty loading) and construction elements with static loads
within the foliation plane (e.g., columns). Minimum
requirements for the thickness of construction elements are
therefore dependent on the dimension of the surface in
relation to the flexural strength. Also lithological and tec-
tonically induced points of weaknesses have to be
considered.
The anisotropy of the slates fabric must be carefully
taken into account in the evaluation of most of their pe-
trophysical properties. The most important fabric elements
in slates are the planar structures, e.g., slaty cleavage, as
they are surfaces of natural weakness, i.e., the preferred
splitting direction in slates. They determine the quality and
uses of these rocks, being the most important property for
the production of thin tiles for roof or fac¸ade cladding.
Therefore, in this investigation the flexural strength is only
measured with the load applied perpendicular to the foli-
ation, the z-direction, as described in Siegesmund and
Du¨rrast (2011).
The presence of linear elements is also of importance
because it may significantly influence the flexural strength.
The lineation can be the result of the intersection of two
planar elements as discussed in the subchapter rock fabrics
and illustrated in Fig. 7 for the dolomitic slates (U33 and
U38A). Slate producers also define the lineation as ‘‘grain’’
(hilo in Spanish and Faden in German), which defines a
penetrative lineation parallel to the x-direction of the
deformation ellipsoid (Garcı´a-Guinea et al. 1998; Wagner
2007). In the Spanish roofing slates (La Fraguin˜a and
Valdemiguel), the grain is defined by deformed grains of
quartz and chlorite.
Considering these two main structural elements, the
flexural strength was determined according to the DIN EN
12372 (1999). In addition the load was applied perpen-
dicular to the bedding and with the lineation parallel
(longitudinal) and perpendicular (transverse) to this linear
load (see Fig. 9). The flexural strength for the studied slates
Table 6 Bacterial growth on the studied slates in different growth
mediums
Sample E. coli (LB/
potato-
dextrose)
B. subtilis (LB/
potato-
dextrose)
A. pullulans (max.
number of colonies/
0.25 mm2)
U33 0/0 3/3 0
U45 1/2 3/2 0
U38A 0/2 3/3 0
U38B 0/0 3/3 0
U38C 0/0 3/3 0
U38D 0/0 3/3 0
U38M 2/3 2/2 0
AP 2/3 0/3 1–2
GA 0/0 3/3 5
AR 0/2 3/3 0
PL 0/0 1/1 0
WS 0/0 3/3 0
120 0/0 3/3 0
150 1/2 3/2 0
PO 0/3 3/2 0
Ul 0/0 2/2 2
U7 0/3 3/3 0–1
U27 0/2 3/3 0–2
The last three samples are sandstone (U1), granite (U7) and marble
(U27) for comparison
LB lysogeny broth and potato-dextrose agar
Evaluation of the growth: 0, no growth; 1–2, weak to moderate; 3,
confluent growth of colonies
1378 Environ Earth Sci (2013) 69:1361–1395
123
varies from 16.4 to 71.9 MPa (Table 7). The lowest value
of 16.4 MPa was measured in the Xisto negro de Foz Coˆa
(PO) in the transversal direction. Piedra laja San Luis (AR)
shows the highest value, 71.9 MPa, for the longitudinal
direction (Mosch 2008).
Wagner (2007) presented a diagram relating the values
of flexural strength obtained for several slates in the two
directions. All slates considered show higher values in the
longitudinal direction (Fig. 9), which is similar to the
current investigation, although in many cases the difference
between both values is within the standard deviation (e.g.,
Ardo´sia Gaspar, Pizarra de techar La Fraguin˜a). Never-
theless, for the Piedra laja verde clara ‘‘macho’’ (U38M),
the flexural strength in the longitudinal direction is 16 %
lower than in the transverse direction.
The most extreme anisotropy is evidenced by Xisto
negro de Foz Coa (PO), which shows a flexural strength
value three times higher in the longitudinal direction than
in the transverse one. This behavior is related to linear
elements of the rock fabric. As described in the subchapter
rock fabric, this rock represents coarser grained domains
with prolate shapes that are limited by solution transfer
foliation and surrounded by fine-grained domains. When
the flexural load is applied parallel to the long axes of this
prolate domain, the solution transfer foliation acts as
cement and raises the strength of the rock. On the other
hand, when the load is applied perpendicular to these
prolate domains, just the contacts between the grains have
to be broken, which are weaker in comparison with the
solution transfer foliation.
A negative correlation occurs between the flexural
strength and water uptake as illustrated by Wagner (2007).
Figure 10 shows this relationship. The samples showing
relatively high water uptake (values higher than 0.60 wt%)
are the ones with the lowest flexural strength (PL). The
samples showing the highest flexural strength have rela-
tively low water uptake; generally below 0.40 wt% as seen
in samples 120, 150 and U33. A1 and A2 are codes defined
in the DIN EN 12326-1. The first comprises the slates with
water uptake below 0.6 wt%, which are freeze–thaw
resistant. The second code is used when a slate has a water
uptake over 0.6 wt%. A freeze–thaw test of 100 cycles
must be performed in order to prove the stability of the
rock in cold climates. In addition, Wagner (2007) takes into
account the NF norm used in France, whereby the resis-
tance to freeze–thaw processes requires a water uptake
below 0.4 wt%.
All the samples analyzed in this study, with the excep-
tions of PL and TH, have water uptakes below 0.4 wt%
(see Fig. 10). They belong to the category A1, and hence,
stable against freeze–thaw phenomena.
Uniaxial compressive strength
Another important parameter to be determined for rocks is
the uniaxial compressive strength (UCS), which is the
maximum compressive stress in one direction until it fails.
This property is especially relevant for rock elements that
have to bear a planar load (Siegesmund and Du¨rrast 2011),
which is seldom the case in slates. Therefore, this property
was determined only for two slate varieties: Piedra laja
negra Rufo Hnos (U45) and Piedra laja gris plomo
(U38B). For these samples the test was performed using the
x–y–z coordinate system (see Table 8) following the DIN
EN 1926 (1999). The UCS values show the maximum
differences between the x- and y-directions, e.g., 191 MPa
in the x-direction and 116 MPa in y-direction for U45
(Table 8). Such anisotropy is related to the influence of the
S2 foliation, which weakens the UCS of the rock in the
y-direction. This is also true for the Piedra laja San Luı´s
(AR), whose values are between 143 MPa (y-direction) and
215 MPa (x-direction) (Mosch 2008).
The UCS values for other slates found in the literature
lack orientation, and therefore, the directional dependence
is unknown. For the Portuguese commercial slates the UCS
values are 144 MPa (Xisto negro de Foz Coˆa, PO) and
159 MPa (Ardo´sia de Canelas, PL) (Laborato´rio Nacional
de Energia e Geologia 2012). The lowest value is 90 MPa
for the Theuma Fruchtschiefer (Natursteinwerk Theuma
AG 2012), while Siegesmund and Stein (2007) found
Fig. 9 Flexural strength transverse to lineation versus flexural
strength parallel to foliation (modified after Wagner 2007)
Environ Earth Sci (2013) 69:1361–1395 1379
123
values of around 173 MPa for the Lotharheil Schiefer. All
these samples can be classified as hard rock (UCS values
higher than 110 MPa), according to the classification
scheme discussed in Siegesmund and Du¨rrast (2011), while
the Theuma Fruchtschiefer belongs to the medium hard
rock.
The Young’s modulus, which relates the strength and
the strain during the UCS measurement as described in
Morales Demarco et al. (2011), ranges from 16 GPa for the
Piedra laja gris plomo (U38B) in the y- and z-directions to
31 GPa for the same variety in the x-direction. The
Young’s modulus values of U45 are higher in the y- and
z-direction than in the x-direction, but the opposite occurs
in sample U38B (see Table 8).
Tensile strength
Tensile strength was measured indirectly by the Brazilian
method as described by Siegesmund and Du¨rrast (2011).
Three directions (x, y and z) with respect to the foliation
and lineation were analyzed for the variety Piedra laja gris
plomo (U38B). In addition, the values determined by
Mosch (2008) for the Piedra laja San Luis (AR) will also be
discussed.
AR shows the highest values for the z- and x-direction,
with 8.0 and 21.4 MPa, respectively (Mosch 2008). How-
ever, U38B shows the highest value in the y-direction
(15 MPa) (Table 8). The average values for both slates are
within the upper and lower quartiles of the tensile strength
values, which were reported for metamorphic rocks in the
data set of Mosch and Siegesmund (2007).
For both commercial slate varieties the values in the
z-direction are the lowest and the ones in the x-direction are
the highest. This anisotropy is to be expected, as these
rocks show a very well-developed slaty cleavage.
Table 7 Mechanical properties of the samples analyzed
Trade name ID Abrasion strength (cm3/50 cm2) Flexural strength (MPa)
x y z Q L
Piedra laja negra, Caorsi Hnos U33 n.d. n.d. 20.6 50.9 ± 5.8 64.1 ± 7.0
Piedra laja negra, Rufo Hnos U45 10.1 7.6 8.1 46.0 ± 6.0 43.6 ± 6.3
Piedra laja ocre U38A n.d. n.d. 10.1 27.7 ± 3.2 49.6 ± 2.2
Piedra laja gris plomo U38B 8.9 10.2 11.9 n.d. n.d.
Piedra laja verde oscura U38C n.d. n.d. n.d. n.d. n.d.
Piedra laja verde clara U38D n.d. n.d. 5.2 n.d. n.d.
Piedra laja verde clara ,,macho’’ U38M n.d. n.d. 10.8 43.5 ± 2.3 36.4 ± 1.3
Piedra laja Puntas del Chafalote UY-108 n.d. n.d. 6.3 n.d. n.d.
Ardo´sia Apiu´na AP n.d. n.d. 19.4 41.0 ± 8.8 58.0 ± 9.8
Ardo´sia Gaspar GA n.d. n.d. 16.8 48.0 ± 11.2 45.1 ± 10.5
Piedra Laja San Luis AR 6.9* 13.3* 21.2* 27.6 ± 3.5 71.9*
Ardo´sia de Canelas PL n.d. n.d. 33.4 23.4 ± 4.4 27.7 ± 4.1
Sauerland Schiefer WS n.d. n.d. 33.4 54.0 ± 3.4 50.7 ± 5.8
Pizarra de techar La Fraguin˜a 120 n.d. n.d. 28.2 60.9 ± 5.9 65.4 ± 3.3
Pizarra de techar La Fraguin˜a 120-b n.d. n.d. n.d. 61.3 ± 3.4 69.1 ± 10.2
Pizarra de techar Valdemiguel 150 n.d. n.d. 31.0 54.3 ± 4.2 65.4 ± 5.3
Xisto negro de Foz Coˆa PO n.d. n.d. 3.6 16.4 ± 3.4 53.3 ± 11.6
Lotharheil Schiefer LO 30.6 (Capon)** 54.2**
Theuma Fruchtschiefer TH 31.0 (mm)? 33.5?
* Data after Mosch (2008); ** data after Siegesmund and Stein (2007); ? data after Natursteinwerk Theuma AG (2012)
Fig. 10 Average flexural strength versus water uptake (modified after
Wagner 2007) (LO data after Siegesmund and Stein 2007, TH data
after Natursteinwerk Theuma AG 2012)
1380 Environ Earth Sci (2013) 69:1361–1395
123
Abrasion strength
The relevance of the abrasion strength in slates, and gen-
erally in all natural stones, is mainly related to their use as
floor tiles and staircases. Floor tiles are exposed to grinding
forces produced by footsteps and walking, and the abrasion
strength test is a method that measures the resistance of a
rock against these forces (see Siegesmund and Du¨rrast
2011).
The abrasion strength was performed using a Bo¨hme
abrasion testing machine as described in the DIN 52108
(1988). The abrasion strength of the xy-plane (parallel to
the foliation) was measured for all samples analyzed, since
this surface is generally used for floor cladding. In the
varieties Piedra laja negra Rufo Hnos, Piedra laja gris
plomo and Piedra laja San Luı´s the xz- and yz-planes were
also measured. The results are shown in Table 7. The
values measured show a large variation, between 3.6 and
33.4 cm3/50 cm2, for the Xisto negro de Foz Coˆa (PO) and
the Sauerland Schiefer (WS), respectively. The samples
that show lower abrasion strength, and therefore higher
values of volume lost, between 28.2 and 33.4 cm3/50 cm2,
are the slates (PL, WS, 120, 150). These rocks show the
highest proportion of normative phyllosilicates, between 61
and 68 %. The highest abrasion strength values exhibited
by the samples with the lowest proportion of normative
phyllosilicates (between 22 and 30 %) are samples PO and
U38D, respectively. Therefore, a negative correlation
between abrasion strength and normative phyllosilicate
proportion is evident when this property is measured par-
allel to the foliation.
In the directions perpendicular to the foliation this cor-
relation is not so clear. Further investigation should be
done to analyze the impact of structural elements in the
abrasion strength of slates.
Based on SEM investigations Strohmeyer (2003) found
that the abrasion strength for highly anisotropic rocks is
lower parallel to the foliation, although the total anisotropy
is less pronounced compared with the flexural strength or
tensile strength. For example, the abrasion resistance for
the slate from Argentina is between 7 and 21 cm3/50 cm2
(67 % anisotropy). In the abrasion test the minerals hardly
show scratching or grinding marks. The minerals appar-
ently suffer crystal fragmentation, which ultimately leads
to the disintegration of the whole mineral assembly by
fabric loosening.
Considering their abrasion strength behavior, slates do
not form a homogeneous group when compared to grani-
toids or quartzites (see Siegesmund and Du¨rrast 2011). The
highest abrasion strength values measured for the slates
(e.g., PO, U38D) allow them to be grouped between the
most resistant dimensional rocks, which are the dolerites,
e.g., the variety Absolute Black with an abrasion resistance
of 2.2 cm3/50 cm2 (Morales Demarco et al. 2011). The
lower abrasion strengths measured in the analyzed slates
(e.g., PL and WS) makes them similar to the group con-
taining clay shale, porous limestone and sandstone (Sieg-
esmund and Du¨rrast 2011).
Thermal and hydric expansion and freeze–thaw tests
The influence of external environmental conditions
(weather, anthropologic factors) is important when con-
sidering the use of slate as a dimensional stone. High
resistance is usually expected in slate, regardless of their
application as roofing or fac¸ade cladding or in garden and
landscaping. The causes of weathering result from thermal
factors, such as changes in temperature and also the impact
of snow and rain. To assess these relationships, thermal,
hydric and freeze–thaw analyses were performed.
Thermal expansion
Changes in temperature can result in volume expansion or
contraction of a stone. Even if the temperature changes are
not large, the repeated heating and cooling of stones could
Table 8 Mechanical properties of the samples analyzed
Trade name ID Uniaxial compressive strength (MPa) Young’s modulus (GPa) Tensile strength (MPa)
x y z x y z x y z
Piedra Laja Negra, Rufo Hnos U45 191 ± 6 116 ± 19 152 ± 23 17 ± 4 18 ± 7 26 ± 6 n.d. n.d. n.d.
Piedra laja gris plomo U38B 153 ± 31 130 ± 29 126 ± 24 31 ± 10 16 ± 11 16 ± 6 19 ± 4 15 ± 3 6 ± 2
Ardo´sia de Canelas PL 159.1* n.d. n.d. n.d. n.d. n.d. n.d.
Xisto negro de Foz Coˆa PO 144.0? n.d. n.d. n.d. n.d. n.d. n.d.
Piedra laja San Luis AR 215* 143* 159* n.d. n.d. n.d. 21.4* 10.7* 8.0*
Lotharheil Schiefer LO 172.6** n.d. n.d. n.d. n.d. n.d. n.d.
Theuma Fruchtschiefer TH 89.8?? n.d. n.d. n.d. n.d. n.d. n.d.
* Data after Mosch (2008); ** data after Siegesmund and Stein (2007)
Environ Earth Sci (2013) 69:1361–1395 1381
123
produce a significant deterioration over time. This holds
true especially in heterogeneous rocks, e.g., with respect to
the rock fabrics and the mineralogical composition.
Thermal expansion measurements of the slates were
performed using a dilatometer (for details see Strohmeyer
2003 or Koch and Siegesmund 2004). In order to simulate
temperature changes comparable to those observed under
natural conditions for building or ornamental stones, the
temperature cycles were fixed at 90 C. The thermal
expansion was measured in three directions: one perpen-
dicular to the foliation (z-direction) and two parallel to it
(x- and y-direction). The values measured for thermal
expansion (Table 9) vary from 7.0 to 13.3 9 10-6 K-1 for
the Ardo´sia de Canelas (PL) and the Piedra laja gris plomo
(U38B), respectively.
In the x- and y-direction the values are generally lower
than in the z-direction (perpendicular to the slaty cleavage),
between 8.5 and 10.3 9 10-6 K-1. This anisotropy is
related to the preferred orientation of the phyllosilicates in
these rocks. In muscovite, for example, the lowest thermal
expansion coefficient is parallel to the crystallographic
a-axis and the highest parallel to the c-axes: 9.9 and
13.8 9 10-6 K-1, respectively, (Fei 1995).
Exceptions are the Ardo´sia Apiu´na (AP) and Ardo´sia de
Canelas (PL). AP is more or less isotropic when comparing
the three measured directions (Table 9), while PL exhibits
anisotropy of around 25 %. Although muscovite crystals
are oriented parallel to the slaty cleavage in the Ardo´sia
Apiu´na (AP), biotite is randomly distributed and it may be
responsible for the more or less isotropic behavior. The
anisotropic behavior of PL can be explained by the chlo-
ritoid porphyroblasts, which are oriented with their long
axes perpendicular, transversal or parallel to the foliation.
Ivaldi et al. (1988) found that chloritoid is an anisotropic
mineral with respect to thermal properties.
The dolomitic slates show slightly higher values per-
pendicular to the foliation than the pelitic and semipelitic
slates. This could be related to a higher thermal expansion
coefficient in dolomite, superposing the effect of the ori-
ented phyllosilicates in the whole rock behavior. Dolomite
shows thermal expansion anisotropy, being higher parallel
to the c-axis than parallel to the a-axes (Reeder and
Markgraf 1986; Weiss et al. 2004).
To summarize, the values given in Table 9 are in
agreement with those compiled by Siegesmund and Du¨rrast
(2011) for slates. According to these authors, their thermal
expansion varies between 9.3 and 12.8 9 10-6 K-1,
showing also higher values in the z-direction.
The residual strain, which is the permanent length
change of a sample after the thermal expansion measure-
ment, is between 0.02 and -0.30 mm/m. The lowest values
are observed in the Piedra laja negra Caorsi Hnos (U33)
and Ardo´sia de Canelas (PL) and the highest in the Ardo´sia
Apiu´na (AP) and Theuma Fruchtschiefer (TH). The The-
uma Fruchtschiefer contains predominantly quartz and
mica and shows high thermal expansion coefficients. These
minerals also have a high volume expansion coefficient.
Feldspar (with a low volume expansion coefficient) is
Table 9 Thermal and hydric expansion of the analyzed samples
Trade name Sample Hydric expansion (mm/m) Thermal expansion coefficient a (910-6 K-1)
x y z x y z
Piedra laja negra, Caorsi Hnos U33 0.08 0.03 0.54 9.0 9.6 11.7
Piedra laja negra, Rufo Hnos U45 0.02 0.02 0.18 9.4 9.7 11.0
Piedra laja ocre U38A 0.01 0.00 0.51 9.4 9.8 10.8
Piedra laja gris plomo U38B 0.03 0.01 0.30 10.3 10.0 13.3
Piedra laja verde oscura U38C 0.02 0.07 0.25 10.1 8.8 10.3
Piedra laja verde clara U38D 0.07 0.04 0.20 9.6 9.4 10.6
Piedra laja verde clara ‘‘macho’’ U38M 0.02 0.06 0.55 9.6 10.2 11.1
Ardo´sia Apiu´na AP 0.47 0.79 1.82 8.6 9.0 8.5
Ardo´sia Gaspar GA 0.10 0.10 0.92 8.6 9.3 10.3
Piedra Laja San Luis AR 0.07 0.03 1.18 9.5* 9.9* 11.8*
Ardosia de Canelas PL 0.17 0.35 6.75 9.4 9.3 7.0
Sauerland Schiefer WS 0.03 0.04 2.68 8.5 9.1 10.7
Pizarra de techar La Fraguin˜a 120 0.01 0.01 1.32 9.1 10.0 12.3
Pizarra de techar Valdemiguel 150 0.01 0.01 1.32 8.9 9.2 11.7
Xisto negro de Foz Coˆa PO 0.03 0.09 0.16 9.5 9.7 9.8
Lotharheil Schiefer LO n.d. 0.09 0.13 n.d. 10.1 10.4
Theuma Fruchtschiefer TH 0.15# n.d. 1.45# 9.8? 9.3? 12.1?
* Data after Mosch (2008); # data after Weiss et al. (2004); ? data after Siegesmund and Du¨rrast (2011)
1382 Environ Earth Sci (2013) 69:1361–1395
123
lacking. The thermal expansion curve of the Theuma
Fruchtschiefer is also characterized by a dehydration
reaction, which is most pronounced perpendicular to the
foliation (residual strain -0.3 mm/m at 20 C) and almost
negligible parallel to the foliation (Weiss et al. 2004).
Hydric expansion
The hydric expansion is a measurement of the dilatation of
a rock when completely submerged in water (Siegesmund
and Du¨rrast 2011). The weathering behavior of dimen-
sional stones is, for these authors, strongly influenced by
the processes involved in hydric expansion together with
the thermal expansion.
This property was also measured using the x, y and
z coordinate system. The values obtained (Table 9 and
Fig. 11) vary between 0.0 in the y-direction for the Piedra
laja ocre (U38A) and 6.75 mm/m in z-direction for the
Ardo´sia de Canelas (PL). The range in x- and y-direction is
between 0.00 and 0.79 mm/m and in the z-direction is
between 0.13 and 6.75 mm/m. As for the thermal expan-
sion this anisotropy is related to the preferred orientation of
the phyllosilicates, the higher proportion of phyllosilicates
in a slate leads to a higher hydric expansion.
In comparison to other dimensional stones, slates show a
wider range of hydric expansion, especially in the case of
pelitic and semipelitic slates (Fig. 12). The values of hygric
expansion shown by the dolomitic slates are comparable to
those of marble, limestone and sandstone with the lowest
hygric expansion (type I, measurements after Hockmann
and Kessler 1950).
Freeze resistance
The freeze resistance is a very important property of
dimensional stones, especially the slates. When the water
uptake is higher than 0.6 wt%, the safeness against freeze
has to be determined in accordance with the DIN EN
12326:1 (2004).
In order to know the weathering stability of the selected
commercial slates in cold climates, a total of 100 freeze–
thaw cycles were carried out. The weight of the samples
and the Young’s modulus were measured every four
cycles.
The mass variation for all the slates considered is very
low, as shown in Fig. 13, between an increase of 0.01 % in
the Ardo´sia Apiu´na (AP), which can be considered an
experimental error, and a decrease of 0.19 wt% measured
Fig. 11 Thermal expansion diagrams for: a Piedra laja gris plomo (U38B) and b Pizarra de techar La Fraguin˜a (120). Hydric expansion
diagrams for: c Piedra laja gris plomo (U38B) and d Pizarra de techar La Fraguin˜a (120)
Environ Earth Sci (2013) 69:1361–1395 1383
123
in the Ardo´sia de Canelas (PL). The samples that showed a
higher weight loss (between 0.12 and 0.19 wt%) are in
increasing order the Piedra laja verde oscura (U38C),
Piedra laja verde clara ‘‘macho’’ (U38M) and the Ardo´sia
de Canelas (PL). In the first two samples the loss of weight
is determined by the dissolution of dolomite on the sample
surface. This phenomenon is also visible in the other
dolomitic slates. Pyrite present as veins and disseminated
shows an incipient oxidation, but no color spots develop
surrounding them. A variation in color is noticed for this
group of slates in the sawed surfaces, but no change is
perceived along the foliation surfaces.
In the Ardo´sia de Canelas an opening of the foliation
surface is noted, as well as orange and white spots due to
the oxidation of pyrite and precipitation of salts (probably
gypsum), respectively. All these processes can explain the
loss of weight in the freeze–thaw experiment. The values
determined for all slates studied are very low compared to
those measured by Ru¨drich et al. (2011) for the Habichts-
wald tuff but similar to those of the Kuaker limestone,
Lobejuen porphyry and Knaupsholz granite.
The values for the Young’s modulus range from 77.7 to
120.7 kN/mm2 in the Ardo´sia Apiu´na (AP) and in the Piedra
laja verde oscura (U38C), respectively (Fig. 13). The vari-
ation of the Young’s modulus ranges between an increase of
up to 10.81 % in the Ardo´sia de Canelas (PL) and a
decrease of up to 24.86 % in the Ardo´sia Apiu´na (AP).
Deposit characterization
Regional mining districts
The dolomitic slate deposits in Uruguay are located 25 km
north of the locality of Pan de Azu´car and about 100 km from
Montevideo. There are two main dolomitic slate mining dis-
tricts in the region (Fig. 14). The northern one is located at the
source of the Arroyo Minas Viejas and is accessible from
Route 60 (Arroyo Minas Viejas district: AMVD). The southern
district is located at the source of the Arroyo Mataojo and
accessible from Route 81 (Arroyo Mataojo district: AMD).
The dolomitic slate deposits are located in the eastern
limb of a regional fold, known as the ‘‘Road 81 syncline’’,
and are related to a second deformation phase. The mining
districts are situated in the center of the Minas Viejas
Association and bound to the east and west with phyllites
and metabasalts. A metagabbro body crops out in the
western boundary of the northern district (AMVD).
A minor slate mining district is represented by
two quarries where the variety Piedra laja rosada con gris
Fig. 12 Hydric expansion of
dolomitic, pelitic and
semipelitic slates in comparison
to different rock types (modified
after Siegesmund and Du¨rrast
2011)
1384 Environ Earth Sci (2013) 69:1361–1395
123
(UY-106) was mined. This district is located 1 km east of
the AMVD but in another lithological association, known
as the Zanja del Tigre-Cuchilla Alvariza Association.
Another slate mining district is located in the Rocha
department, represented by the slate variety Piedra laja
Rocha (UY-108) and belonging to the lithological unit of
the Rocha Group.
The AMVD is 3 km long in a NE–SW direction and
300 m wide. This district is characterized by the presence
of dolomitic slates showing light and dark green, red, gray
and bluish gray colors. A total of 18 quarries of different
sizes are located in this district, in which just four are being
actively mined. About 3 km to the southwest the Arroyo
Mataojo district is located. It extends further to the
southwest for about 4 km and is 500 m wide. Five quarries
of dark gray and black dolomitic slates are found in this
district, but at the present only one is active.
The dolomitic slate deposits are characterized by their
elongated shape parallel to the S0–1 foliation, which makes
their mining similar to the quarrying of dikes (e.g., dolerite).
Since the slate deposits are related to strata with a defined
composition, they can be defined as stratabound deposits in
the sense of Canavan (1973). To define a dolomitic slate
deposit is necessary not only to find the characteristic mineral
composition, but also an ensemble of structural factors that
will allow their profitable mining (e.g., parallelism between
S0–1 and S2, absence of highly folded sectors).
The mining districts have a width of 300–500 m, how-
ever, the individual slate bodies can range between 8 and
50 m in width, but generally most show widths of around
12 m. Their length varies between 60 and 150 m and the
current exploitation depth ranges between 6 and 15 m.
The northwest walls tend to be unstable, due to the fact that
the foliation dips around 80 to the northwest. In active
quarries those walls are controlled daily to prevent collapse.
The dolomitic slates deposits in Uruguay occur in the
greenschist facies volcano-sedimentary Lavalleja Group,
which forms part of the Dom Feliciano Belt in Uruguay.
These deposits are, therefore, controlled by the regional
structures that affect all the lithologies comprising this
group.
Structural framework and controlling factors
of the deposit
The structural framework of the studied area was investigated
in detail by Midot (1984), who recognized three phases of
Fig. 13 Mass variation after 100 freeze–thaw cycles for: a commercial dolomitic slates, b commercial pelitic and semipelitic slates. Young’s
modulus variation after 100 freeze–thaw cycles for: c commercial dolomitic slates, d commercial pelitic and semipelitic slates
Environ Earth Sci (2013) 69:1361–1395 1385
123
deformation. The first phase (D1) generated the foliation S1
with the oriented recrystallization of the phyllosilicates and
the stretching of other minerals such as quartz, feldspar and
dolomite. S1 is described as an axial plane foliation resulting
from isoclinal folding. Due to transposition, the primary
foliation of these rocks (S0) is similar to the foliation S1.
Midot (1984) defines these foliations as S0–1, because with
few exceptions it is very difficult to distinguish them both
(e.g., in intrafolial microfolds). The S0–1 is the slaty cleavage
that characterizes the dolomitic slates and creates the con-
dition for their extraction. The cleavage dips between 70 and
90 to the NW with a NNE strike (Figs. 15, 16).
Boudinage of the carbonate and quartzite layers inter-
layered in the dolomitic slate body also belongs to the D1
(Fig. 17a). Generally, the boudins are between 2 and 5 cm
thick, and show extension in two directions perpendicular
to one another, which produce irregularities in the surface
of the slate. These boudins are more frequent in the
AMVD, and thus create problems for the extraction of the
mined slates in this district. Another structural element
related to this D1 is the mineral lineation L1, as evidenced
by the alignment of fine-grained chlorite and sericite
aggregates in the foliation plane.
The second deformation phase defined by Midot (1984) is
a folding event, which generated folds of millimeters to
kilometric in magnitude. The last ones are the most fre-
quently recognized, e.g., the Road 81 syncline, which is one
of the major folds acknowledged in the area. Midot (1984)
described the structures developed in the dolomitic slates in
this phase as fracture cleavage, which is the old term for
disjunctive foliation or cleavage. A spaced cleavage is
characterized by the presence of microlithons between the
cleavage domains (Passchier and Trouw 1996). Disjunctive
foliation can evolve to ‘‘strain–slip schistosity’’ or, using a
term with no genetic connotations: crenulation cleavage
(Passchier and Trouw 1996). This disjunctive foliation or
crenulation cleavage is an axial plane foliation (S2) that
intensely deforms the S0–1, when the angle between both
foliations is near 90 (in the hinges of the folds of D2). When
the angle between both foliations is small, the S0–1 surface is
not affected and S2 is parallel to S0–1. There is no evidence of
recrystallization associated to this deformation phase D1.
Midot (1984) described the D2 microfolds in the slates
as being of two types: kink (or chevron folds) and others
with more rounded and open hinges. The kink folds are
asymmetric and they negatively affect the mining of the
Fig. 14 Location of dolomitic
slate mining districts in
Uruguay
1386 Environ Earth Sci (2013) 69:1361–1395
123
deposit, only when their amplitude is larger than 2.5 cm
(Fig. 17b, c). However, these kink folds generally have
smaller amplitudes (on the order of 0.5 cm) and larger
wavelengths ([4 m), and therefore they do not affect the
extraction of the slates.
The lineation L2 develops as the foliations S0–1 and S2
intersect and is parallel to the fold axes. The folds
belonging to the second type are decimeters in size, but
composed of a multitude of millimeter-sized microfolds
that generate an embossing of the S0–1 surface. The axes of
these microfolds produce a microfolding or intersection
lineation, also called L2 by Midot (1984).
Another element that negatively affects the quality of the
mined slate in the deposits is the foliation S2. When the angle to
the foliation S0–1 is less than 10, scales will develop on the S0–1
surface. Also when the angle between S0–1 and S2 is greater
than 30, the mining will be negatively affected because the
slate does not split as easily through the S0–1 foliation.
Structures of the last deformation phase (D3) are only locally
found near areas with high brittle deformation. These structures
represent a second disjunctive foliation (S3) that deforms both
S2 and S0–1. The S3 is vertical and is sometimes accompanied
by inverse fractures dipping to the west. The frequency and
intensity of S3 determines in some cases the length of the
deposits, since this S3 foliation frequently crosscuts them.
To summarize, all these structural factors control the
following aspects of the deposits:
(a) width of the deposits, due to the occurrence of
strongly folded sectors that progressively limit the
mining on both lateral walls of a quarry;
(b) length of the deposits, which determines either the
occurrence of E–W strike–slip faults (dextral and
sinistral) and/or boudins affecting decameter-scaled
dolomitic slate bodies, both elements disrupting the
continuity of these bodies;
(c) depth of the mining, controlled by the dip angle of the
foliation S0–1, which determines the stability of the
northwestern quarry wall.
To investigate the relationship between geochemistry of
the different dolomitic slates and their mechanical response
to the deformation phases, several samples have been ana-
lyzed by XRF (Tables 10, 11). Samples were collected from
quarry G119 (the commercial varieties U38B and U38C)
and in quarry G120 (U38D and U38M), located 10 m to the
southeast from the first quarry. The samples U38B, U38C
and U38D show a very good fissility along the foliation S0–1,
whereas the fissility is very poor in sample U38M. This last
sample is characterized by the abundance of isoclinal folds
and its inhomogeneity, defined by the intercalation of layers
with coarse-grained quartz and pyrite grains, and layers with
similar composition and fabric as U38D. When comparing
the geochemistry of these three rocks, the main difference is
in the composition of U38B, which shows more SiO2 and
less MgO, CaO and CO2 than the other three varieties. In the
case of U38M it is highly probable that the coarser grained
layers affect the rheology of the rock, producing more folds
and a well-developed S2.
Another example is given by quarry (G115) where the
samples (U38A and UY-54) are not affected by folds, when
compared with a sample located 5 m southeast from the
quarry wall and strongly folded (UY-87). These three rocks
do not show any significant differences in their geochem-
istry or petrography, but they do show variations in the
quality as a marketable slate.
The structural development in the dolomitic slate body
(e.g., folds, boudins, faults) appears to be controlled by the
preexisting rock fabric and the deformation regime. The
joint systems that developed later do not necessarily affect
the mining of the slates. They are generally orthogonal to one
another (Fig. 17f) and their frequencies allow the acquisition
Fig. 15 Stereonets showing the structural elements in the dolomitic slate deposits (lower hemisphere): a foliations; b fold axes and lineations;
c joint sets (1, 2,…,13 multiples of random distribution)
Environ Earth Sci (2013) 69:1361–1395 1387
123
of sufficiently large blocks (up to 50 cm perpendicular to the
foliation and up to 4 m2 parallel to the foliation).
Mining techniques in Uruguay
The techniques used in Uruguay today for exploiting dolomitic
slates do not include the most modern ones, such as the dia-
mond wire technique. Instead small explosive charges are used
to remove relatively large blocks (up to 4 m3). The direction of
mining is perpendicular to the foliation and always from
above. These blocks are reduced to smaller blocks with a
pneumatic hammer in the quarry and then transported to cut-
ting shed (Fig. 18a, b). There the blocks are cut to preset
dimensions (e.g., 30 9 40 cm) and afterwards split by hand to
a desired thickness (generally 16 mm) (Fig. 18c, d).
Economic aspects
Estimation/evaluation of the deposits
Dolomitic slate deposits are characterized by their elon-
gated shape and relatively small sizes. The three spatial
dimensions (width, length and depth) are limited by the
structural controlling elements that define the geometrical
distribution of the lithology of interest. No data of conti-
nuity with depth exists for the dolomitic slate deposit,
however, based on the vertical exposure of the dolomitic
slate body, it probably continues for at least 50 m in depth.
This is also the maximum depth for mining without taking
the safety precautions into consideration, especially in cases
where the deposits are very narrow. The possible occur-
rence of inverse fractures from the deformation D3 (Midot
1984) could interrupt the continuity of the deposit at depth.
A typical dolomitic slate deposit from the northern district
was evaluated for its economic potential, whereby the results
can be extrapolated to the other deposits in both mining
districts. The chosen deposit, composed of quarries G118 and
G119, is bound to the northeast and south by strike–slip
faults, having a length of 400 m. These strike–slip faults are
recognizable in aerial photos and satellite images. In the field
small valleys are recognizable in the deposit boundaries,
which indicate the presence of faults. Furthermore, explor-
atory quarries have been opened near these faults and the
mining was discontinued due to intensive folding (related to
the major regional folds) or a very well-developed S2 folia-
tion (with an angle to S0–1 of 30), or both. The deposit width
is 12 m, being bounded by folded zones to the northwest and
southeast, which produces a loss of fissility and the mining
there becomes unprofitable. The raw blocks extracted from
these folded zones are not suitable for the production of
marketable slabs with at least 30 cm in length.
The deposit is separated by a fault along the middle of
its length, which leads to a cessation of mining at about
30 m. The lithologies are the same on both sides of the
fault, as well as the dip and direction of the main foliation.
Both sectors of the deposit have been successfully mined;
the northern one corresponds to the inactive quarry G118,
and the southern one to the active quarry G119.
Two color varieties are available in this deposit: Piedra
laja gris plomo (U38B) cropping out as a 5-m ‘‘layer’’ on the
Fig. 16 a Joint sets in the black dolomitic slate (U33, Caorsi Hnos
Quarry). b Stereonet depicting the three main joint sets. c Histogram
showing joint set distribution
1388 Environ Earth Sci (2013) 69:1361–1395
123
northwest side and Piedra laja verde oscuro (U38C), which is
exposed as a 7-m ‘‘layer’’ on the southeast side. These vari-
eties are designated first quality (Q1), meaning that they
represent an excellent fissility and the plates obtained by
splitting are very thin (16 mm). On both sides of the deposit
varieties with inferior quality can be mined. The second
quality is defined as Q2, having this variety an angle between
S0–1 and S2 larger than 30, and therefore, a non-completely
parallel foliation and splitting in wider plates. The third
quality, Q3, is a variety with bad fissility due to the occurrence
of folds (kink bands) and a stepped foliation surface.
Currently the depth of the deposit is 15 m. Considering
that the foliation S0–1 dips about 80 to the northwest and
the deposit has a maximum width of 12 m, the maximum
depth to which the mining could proceed without consid-
ering the safety risks would be 50 m. A simplified model of
the impact of the foliation dip and how it would influence
the mining is illustrated in Fig. 19. Others factors also
influence the depth of mining. The depth of the water table
plays an important role in mining since the annual rainfall
in Uruguay is relatively high, about 1,200 mm, which
affects the pumping of water in a quarry at a 50-m depth.
The rate of exploitation of marketable products with a
quality level Q1 is relatively low in comparison to other
dimensional stone deposits. The current yield of 7 %
in dolomitic slates, based on international comparable
Fig. 17 Structural elements negatively affecting the dolomitic slate
deposits in Uruguay. a Carbonate boudins with quartz necks.
b Foliation in slate showing large amplitudes and very frequent kink
bands. c Highly folded slate. d Scales develop where S0–1 and S2
intersect at a low angle of 8. e Main foliation indicated by pencil
(S0–1) and posterior foliation (S2) intersecting at approximately 30.
f Joint systems: subhorizontal, subvertical perpendicular and parallel
to the foliation
Environ Earth Sci (2013) 69:1361–1395 1389
123
deposits and the mining efficiency according to the local
producers, could be considerably improved by the com-
mercialization of the Q2 and Q3 varieties.
For the calculation of the reserve in the southern section
of the deposit (G119) a length of 200, a width of 12 and a
depth of 20 m are considered. From a total volume of
48,000 m3 a yield of 7 % is expected. Therefore, the
dolomitic slate reserves in quarry G119 would be
3,360 m3. For the northern section of the deposit (G118)
the length considered is 100 m, the width and depth remain
the same as in the southern section. Considering the yield
of 7 % again, the estimated reserves for this section are
1,680 m3. Taking into account that the material extracted
will be split into slabs of 16 mm thickness, a production of
315,000 m2 could be expected from this deposit.
For a mining depth of 50 m the total production of the
deposit would be 12,600 m3 or 787,500 m2 (for 16-mm-thick
slabs) considering a yield of 7 %. Due to the instability of the
northwest wall, a large amount of waste material has to be
extracted in order to reach a depth of 50 m. Around 66,150 m3
have to be extracted, so that around 15 % of this material could
Fig. 18 Mining activities in a typical dolomitic slate quarry in the
Arroyo Minas Viejas district (AMVD) in Uruguay (Company
Carmine Rufo). a Active slate quarry where Piedra laja ocre
(U38A) is mined. b Active slate quarry where Piedra laja gris plomo
(U38B) and verde clara (U38C) are mined. c Sawing of selected
material to standard sizes. d Manual splitting of small tiles for wall
cladding
Fig. 19 Idealized model of a slate deposit with waste material to be
extracted
1390 Environ Earth Sci (2013) 69:1361–1395
123
be commercialized as second and third quality slate (Q2 and
Q3) for use as rubble stone and stone stairs. This would make
an additional production of 9,920 m3.
According to DINAMIGE (2012), the total production
of slates in the year 2007 was 2,073 m3 consisting of the
black and colored slate varieties, where the volume pro-
duction of both varieties are equal. When considering a
slab thickness of 16 mm again, the production of colored
slates is almost 75,000 m2. Around 60 % of the annual
colored slate production presumably comes from the
deposit described and analyzed above. The mining of this
deposit produces 45,000 m2 annually and when the mining
only goes to a depth of 20 m, the life of the quarry would
be 7 years. Using a depth of 50 m would allow the deposit
to be active for a period of 17 years and 6 months.
To increase the 7 % yield, the raw material should be
reassessed in order to transform it into a marketable product.
The raw material is defined as quality Q2 and Q3. The alter-
native uses for Q2 and Q3 are rubble stones, stone stair treads,
thick polygonal slabs and irregular material for gardens (e.g.,
as stepping stones) and landscaping stones. The raw material
that is intensively jointed, and therefore, small in size can be
commercialized as tiles for indoor or outdoor cladding.
Intensively folded material can also be applied as stone block
steps. All these products can be sold on the local, regional
(Latin America) and international markets. Other alternative
uses for the local market are those which utilize the waste
material resulting from the sawing. These small pieces can be
reselected for the design of mosaics, for example, or be used as
raw material for road construction or maintenance. For the
local situation in Uruguay this has no relevancy, but the
dolomitic slates show little impact to freeze–thaw and could be
used without any problems in countries with colder climates.
The external factors that influence the mining costs are
mainly energy (fuel), purchase of machinery, pumping of
water (at 30 m depth), salaries, cost for mining preparation and
organization, environmental costs and royalty (government
taxes). Credit costs are also considered in the economic costs as
they are of fundamental importance for the initial investments.
Acknowledgments We would like to thank Dipl.-Ing. Peter
Machner, Dr. Axel Wetzel and Matthias Gehrke for the abrasion
measurements in the laboratories of the AMPA (Amtliche Material-
pru¨fanstalt fu¨r das Bauwesen) of the University of Kassel, Dr. Rudolf
Naumann for the geochemical measurement in GFZ (GeoFors-
chungsZentrum) in Potsdam, Dr. Wolfgang Wagner, Dr. Dieter Jung
and Andreas Ja¨ger for their support and the permission to use the
software Slatenorm for the plotting of geochemical data and Dipl.-
Min. Dirk Kirchner for the freeze resistant tests. In Uruguay thanks to
the Rufo family which allowed us the study of their quarries and
facilitated us samples. To Dr. Miguel Basei, Dr. Axel Vollbrecht,
Harald Tonn, Dr, Michael Huppert, Dr. Cornelius Fischer, Dr. Klaus
Wemmer, Dipl. Geol. Frithjof Bense, Dipl. Geol. Stefan Lo¨bens and
Gu¨nter Tondock we are very grateful for their help in the collection or
preparation of samples and for the fructiferous discussions. Special
thanks also go to the students and friends for their help.
P. Oyhantc¸abal thanks the support of the Deutscher Akadamischer
Austausch Dienst (DAAD research grant A/12/04666) and the Uni-
versidad de la Repu´blica of Uruguay. M. Morales Demarco is grateful
to DAAD long-term fellowship (A/07/98548).
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
Appendix
See Appendix Tables 10, 11, 12.
Table 10 Major element geochemistry of the investigated slates
Sample SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 H2O CO2 Sum
U33 42.64 0.405 9.58 3.51 0.06 9.81 11.12 \0.01 3.21 0.094 2.15 16.91 99.49
U45 50.9 0.410 10.2 3.38 0.08 8.52 8.42 0.88 2.24 0.130 2.25 12.39 99.76
U38D 30.45 0.244 6.49 1.9 0.06 12.8 17.23 \0.01 2.04 0.065 1.61 26.92 99.81
U38C 31.22 0.235 6.07 2.58 0.08 12.49 17.16 \0.01 1.84 0.068 1.48 26.68 99.90
U38B 42.48 0.324 8.64 4.08 0.06 9.1 11.88 \0.01 2.88 0.088 1.79 18.41 99.74
U38A 37.44 0.321 7.82 2.52 0.09 10.43 14.54 \0.01 2.69 0.082 1.45 22.43 99.81
U38M 32.42 0.258 6.81 2.23 0.05 12.38 16.25 \0.01 2.09 0.065 1.6 25.38 99.54
UY-19 30.56 0.237 6.14 2.95 0.09 12.84 17.12 \0.01 1.83 0.07 1.58 26.45 99.87
UY-21 29.15 0.23 6.2 3.32 0.09 12.24 17.66 \0.01 2.14 0.071 1.25 27.5 99.85
UY-45 43.55 0.373 8.47 2.03 0.05 10.82 11.84 \0.01 2.35 0.127 2.14 18.04 99.79
UY-54 34.13 0.276 6.92 2.74 0.10 11.26 16.15 \0.01 2.36 0.083 1.38 24.48 99.87
UY-85 40.62 0.271 6.25 3.44 0.44 8.28 14.96 \0.01 2.36 0.144 1.37 21.54 99.68
UY-87 33.43 0.271 6.56 2.93 0.09 11.27 16.16 \0.01 2.33 0.074 1.4 25.41 99.92
UY-88 37.33 0.299 6.79 3.27 0.11 11.59 14.15 \0.01 1.84 0.1 1.9 21.94 99.32
UY-90 30.03 0.236 6.12 2.54 0.08 12.27 17.58 \0.01 1.97 0.074 1.27 27.69 99.86
Environ Earth Sci (2013) 69:1361–1395 1391
123
Table 11 Trace element geochemistry of the investigated slates
Sample Ba Cr Ga Nb Ni Rb Sr V Y Zn Zr
U33 486 66 13 13 43 106 61 36 20 26 130
U45 313 64 14 11 26 85 45 49 18 58 115
U38D 299 43 10 \10 24 72 78 32 17 16 63
U38C 414 41 \10 \10 29 71 90 22 18 18 56
U38B 1,009 47 10 10 35 119 73 43 19 16 77
U38A 728 49 \10 11 34 95 55 37 17 13 99
U38M 343 45 \10 \10 41 76 80 34 19 20 63
UY-19 675 44 \10 \10 39 73 93 29 18 24 54
UY-21 659 39 \10 \10 36 88 91 31 19 19 56
UY-45 456 57 11 12 56 90 80 35 14 33 82
UY-54 556 50 \10 10 36 83 58 35 19 12 70
UY-85 315 39 \10 10 22 97 120 16 40 12 83
UY-87 477 48 \10 11 37 82 85 29 18 14 77
UY-88 3,204 49 \10 12 42 69 197 35 19 42 72
UY-90 451 48 \10 10 41 77 105 30 20 20 58
UY-106 443 94 14 22 54 145 70 78 18 67 128
UY-108 719 57 22 18 37 232 137 70 30 57 166
AP 598 70 23 18 56 174 138 85 44 86 232
AR 591 74 25 19 49 212 79 103 38 100 139
PL 536 135 31 20 85 158 177 169 39 169 99
GA 727 88 22 20 50 211 130 99 41 100 212
WS 440 147 25 19 96 167 110 130 34 101 180
120 691 104 25 21 56 144 140 122 42 106 232
150 711 106 24 22 56 149 139 135 41 102 223
PO 769 66 19 18 38 144 225 76 37 67 277
LO 543 44 15 17 28 121 263 40 38 46 408
Table 10 continued
Sample SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 H2O CO2 Sum
UY-106 56.27 0.953 12.56 6.52 0.11 6.11 4.09 \0.01 3.73 0.147 3.42 5.9 99.81
UY-108 60.92 0.548 17.22 4.78 0.09 1.57 1.44 1.9 4.64 0.139 2.24 4.11 99.60
AP 60.24 0.754 15.37 5.39 0.29 1.95 3.87 2.24 3.4 0.211 2.78 3.2 99.70
AR 61.31 0.742 17.53 7.43 0.17 2.51 0.39 1.37 4.26 0.117 3.24 0.53 99.60
PL 49.91 1.007 24.49 10.21 0.08 2.4 0.24 0.75 3.16 0.179 5.46 1.22 99.10
GA 62.55 0.825 17.28 6.5 0.09 2.13 0.74 1.95 4 0.161 3.27 0.19 99.69
WS 56.43 0.912 18.58 7.63 0.14 2.86 0.87 0.89 3.48 0.136 4.4 2.69 99.02
120 57.83 1.009 18.92 7.75 0.08 2.47 0.62 1.52 3.41 0.192 4.04 1.59 99.43
150 57.71 1.016 18.95 7.46 0.08 2.38 0.57 1.53 3.46 0.191 4.49 1.61 99.44
PO 66.93 0.753 14.61 4.6 0.05 2.12 1.33 2.52 3.42 0.14 2.12 0.83 99.42
LO 71.07 0.581 10.86 3.34 0.08 1.18 3.5 1.25 2.79 0.132 1.82 3 99.60
1392 Environ Earth Sci (2013) 69:1361–1395
123
Table 12 Normative minerals calculated using Slatenorm.exe
Sample qz mu pa or ab an fac mac mc
U33 26.42 24.07 0.00 2.32 0.00 0.00 0.00 0.00 6.17
U45 32.43 19.03 5.38 0.00 3.79 0.00 0.00 0.00 7.90
U38A 25.75 19.29 0.00 2.51 0.00 0.00 0.00 0.00 0.90
U38B 28.65 21.79 0.00 1.96 0.00 0.00 0.00 0.00 2.70
U38C 22.48 15.69 0.00 0.00 0.00 0.00 0.21 0.09 1.51
U38D 21.13 16.90 0.00 0.37 0.00 0.00 0.00 0.00 2.02
U38M 22.73 17.84 0.00 0.00 0.00 0.00 0.04 0.03 2.20
UY-19 21.36 15.55 0.00 0.00 0.00 0.00 0.38 0.23 2.17
UY-21 19.64 15.26 0.00 2.06 0.00 0.00 0.00 0.00 -0.36
UY-45 31.22 19.97 0.00 0.00 0.00 0.00 0.67 1.76 5.27
UY-54 23.39 17.13 0.00 2.04 0.00 0.00 0.00 0.00 1.19
UY-85 30.76 14.59 0.00 3.90 0.00 0.00 0.00 0.00 -1.62
UY-87 23.61 15.89 0.00 2.77 0.00 0.00 0.00 0.00 -0.65
UY-88 27.57 15.73 0.00 0.00 0.00 0.00 1.29 1.20 3.14
UY-90 21.79 15.69 0.00 0.76 0.00 0.00 0.00 0.00 -0.69
UY-
106
36.01 31.82 0.00 0.00 0.00 0.00 0.68 0.68 7.73
UY-
108
31.58 35.89 0.00 2.69 16.28 0.00 0.00 0.00 1.55
AP 29.59 29.17 0.51 0.00 18.87 1.41 0.00 0.00 4.53
GA 30.22 34.23 0.81 0.00 16.14 2.40 0.00 0.00 4.94
AR 31.08 36.43 4.22 0.00 8.82 0.91 0.00 0.00 5.82
PL 28.16 27.62 9.56 0.00 0.00 0.00 13.60 8.57 0.00
WS 33.79 30.44 11.35 0.00 0.00 0.00 5.61 3.59 3.74
120 30.37 29.58 18.96 0.00 0.19 1.17 0.00 0.00 5.81
150 30.39 30.17 18.47 0.00 0.68 1.18 0.00 0.00 5.62
PO 33.38 18.95 0.00 7.30 21.68 5.52 0.00 0.00 4.94
LO 50.55 20.76 0.00 2.20 10.72 1.49 0.00 0.00 2.74
TH* 35.24 33.31 13.70 0.00 0.00 0.34 2.00 0.81 3.40
Sample fc ct cc dol sid pt gr ilm ap sum
U33 4.73 0.00 1.92 32.97 0.00 0.23 0.18 0.79 0.21 100
U45 4.73 0.00 2.10 23.39 0.00 0.04 0.12 0.78 0.30 100
U38A 3.60 0.00 0.84 46.21 0.00 0.00 0.10 0.61 0.19 100
U38B 6.00 0.00 1.31 36.65 0.00 0.00 0.11 0.61 0.21 100
U38C 3.65 0.00 1.14 54.48 0.00 0.00 0.12 0.46 0.16 100
U38D 2.67 0.00 0.98 55.13 0.00 0.04 0.12 0.46 0.16 100
U38M 2.96 0.00 0.48 52.76 0.00 0.19 0.11 0.50 0.16 100
UY-19 3.87 0.00 1.02 54.40 0.00 0.23 0.17 0.46 0.16 100
UY-21 4.95 0.00 0.58 57.05 0.00 0.04 0.18 0.44 0.16 100
UY-45 2.20 0.00 0.90 36.89 0.00 0.00 0.12 0.71 0.30 100
UY-54 4.02 0.00 1.97 49.37 0.00 0.00 0.16 0.53 0.19 100
UY-85 5.76 0.00 4.12 41.52 0.00 0.00 0.14 0.52 0.33 100
UY-87 4.20 0.00 0.00 53.22 0.08 0.04 0.16 0.52 0.16 100
UY-88 3.72 0.00 0.47 45.75 0.00 0.19 0.14 0.58 0.23 100
UY-90 3.57 0.00 0.00 57.92 0.16 0.00 0.18 0.46 0.16 100
UY-106 8.43 0.00 0.57 11.86 0.00 0.00 0.04 1.82 0.35 100
UY-108 0.79 0.00 0.00 4.18 5.62 0.00 0.03 1.06 0.33 100
AP 7.80 0.00 6.00 0.00 0.00 0.02 0.16 1.44 0.49 100
Environ Earth Sci (2013) 69:1361–1395 1393
123
References
Allaby A, Allaby M (1990) The concise Oxford dictionary of earth
sciences. Oxford University Press, Oxford
Basei MAS, Siga O Jr, Masquelin H, Harara OMM, Reis Neto JM,
Preciozzi F (2000) The Dom Feliciano Belt of Brazil and
Uruguay and its Foreland Domain the Rio de la Plata Craton:
framework, tectonic evolution and correlation with similar
provinces of Southwestern Africa. In: Cordani UG, Milani EJ,
Thomaz Filho A, Campos DA (eds) Tectonic evolution of South
America, Rio de Janeiro, pp 311–334
Basei MAS, Frimmel HE, Nutman AP, Preciozzi F (2008) West
Gondwana amalgamation based on detrital zircon ages from
Neoproterozoic Ribeira and Dom Feliciano belts of South
America and comparison with coeval sequences from SW
Africa. In: Pankhurst RJ, Trouw RAJ, de Brito Neves BB, De
Wit MJ (eds) West Gondwana: Pre-Cenozoic correlations across
the South Atlantic Region, vol 294. Geological Society, Special
Publications, London, pp 239–256
Bentz A, Martini HJ (1968) Lehrbuch der Angewandten Geologie,
Band 2, 1: Methoden zur Erforschung der Lagersta¨tten von
Erzen, Kohle, Erdo¨l, Slazen, Industrie-Mineralen und Steinen
und Erden. Sttutgart (Enke)
Bossi J, Campal N (1992) Magmatismo y tecto´nica transcurrente
durante el Paleozoico Inferior en Uruguay. In: Gutierrez Marco
JC, Saavedra J, Rabano I (eds) Paleozoico Inferior de Iberoame´-
rica. Universidad de Extremadura, Espan˜a, pp 345–356
Bossi J, Ferrando L (2001) Carta Geolo´gica del Uruguay a escala
1/500 000, v. 2.0, versio´n digital. Ed. Ca´tedra de Geologı´a,
Facultad de Agronomı´a, Montevideo
Bossi J, Ferna´ndez A, Elizalde G (1965) Predevoniano en el Uruguay
Brito Neves BB, Cordani U (1991) Tectonic evolution of South
America during the Late Proterozoic. Precambrian Res 53:23–40
Bucher K, Frey M (2002) Petrogenesis of metamorphic rocks, 7th
edn. Springer, New York
Canavan F (1973) Notes on the terms ‘stratiform’, ‘stratabound’ and
‘stratigraphic control’ as applied to mineral deposits. J Geol Soc
Aust 19(4):543–546
Card N (2010) Colour, cups and tiles—recent discoveries at the Ness
of Brodgar. Past—The Newsletter of the prehistoric society, no
66, London
Comunita` Economica Europea—Uruguay. Piedras Ornamentales del
Uruguay. La Cartotecnica, Rovereto
Coronel N, Spoturno J, Go´mez C, Heinzen W, Mari C, Roth W,
Theune C, Stampe W (1987) Carta de los recursos Minerales no
matalı´feros del Uruguay. DINAMIGE, Montevideo, Uruguay
de Almeida FFM (1971) Geochronological division of the Precam-
brian of the South America. Rev Bras Geol 1(1):13–21 San
Paulo, Brasil
DIN 52108 (1988) Pru¨fung anorganischer nichtmetallischer Werkst-
offe; Verschleißpru¨fung mit der Schleifscheibe nach Bo¨hme.
Beuth, Berlin
DIN EN 12372 (1999) Pru¨fverfahren fu¨r Naturstein—Bestimmung
der Biegefestigkeit unter Mittellinienlast. Beuth, Berlin
DIN EN 1926 (1999) Pru¨fverfahren fu¨r Naturstein—Bestimmung der
Druckfestigkeit. Beuth, Berlin
DIN EN 12326-2 (2000) Schiefer und andere Natursteinprodukte fu¨r
u¨berlappende Dachdeckungen und Außenwandbekleidungen.
Teil 2: Pru¨fverfahren. DIN Deutsches Institut fu¨r Normung
e.V., Beuth, Berlin
DIN EN 13775 (2001) Pru¨fverfahren fu¨r Naturstein—Bestimmung
der Wasseraufnahme bei atmospha¨rischem Druck. Beuth, Berlin
DIN EN 12326-1 (2004) Schiefer und andere Natursteinprodukte fu¨r
u¨berlappende Dachdeckungen und Außenwandbekleidungen.
Teil 1: Produktspezifikation. DIN Deutsches Institut fu¨r Nor-
mung e.V., Beuth, Berlin
DINAMIGE (Direccio´n Nacional de Minerı´aa y Geologı´a) (2012)
http://www.dinamige.gub.uy. Last accessed March 2012
Fei Y (1995) Thermal expansion. In: Ahrens T (ed) Mineral physics
crystallographic: a handbook of physical constants. American
Geophysical Union Books Board, Washington DC
Fischer C, Kaufhold S, Wedekind W, Dohrmann R, Karius V,
Siegesmund S (2011) Weathering of Fruchtschiefer building
stones: mineral dissolution or rock disaggregation? Environ
Earth Sci 63:1665–1676. doi:10.1007/s12665-011-0986-z
Fluhr JW, Gloor M, Merkel W, Warnecke J, Ho¨ffler U, Lehmacher
W, Glutsch J (1998) Antibacterial and sebosuppressive efficacy
of a combination of chloramphenicol and pale sulfo-
nated shale oil. Multicentre, randomized, vehicle-controlled,
double-blind study on 91 acne patients with acne papulopustul-
osa (Plewig and Kligman’s grade II–III). Arzneimittelforschung
48(2):188–196
Fragoso Ce´sar R (1980) O crato´n do Rı´o de la Plata e o Cintura˜o Dom
Feliciano no Escudo Uruguaio-Sul-Riograndense. In: XXXI
Congresso Brasileiro de Geologı´a, Anais, Brasil, vol 5,
pp 1879–2892
Table 12 continued
Sample fc ct cc dol sid pt gr ilm ap sum
GA 9.05 0.00 0.09 0.00 0.00 0.02 0.13 1.60 0.38 100
AR 10.67 0.00 0.09 0.00 0.00 0.13 0.11 1.42 0.28 100
PL 0.00 9.12 0.00 0.01 0.10 0.44 0.40 1.98 0.43 100
WS 6.38 0.00 0.56 1.31 0.00 0.58 0.53 1.79 0.34 100
120 10.73 0.00 0.26 0.00 0.00 0.13 0.39 1.97 0.45 100
150 10.29 0.00 0.16 0.00 0.00 0.15 0.43 2.00 0.45 100
PO 5.95 0.00 0.09 0.00 0.00 0.21 0.20 1.45 0.33 100
LO 4.41 0.00 5.48 0.00 0.00 0.08 0.15 1.12 0.31 100
TH* 9.23 0.00 0.00 0.00 0.00 0.00 0.00 1.73 0.23 100
Data from Theuma Fruchtschiefer (TH*) after Fischer et al. (2011)
ab albite, an anorthite, ap apatite, cc calcite, ct chloritoid, dol dolomite, fac daphnite, fc greenalite, gr graphite, ilm ilmenite, mac amesite, mc
serpentine, mu muscovite, or orthoclase, pa paragonite, pt pyrite, qz quartz, sid siderite
1394 Environ Earth Sci (2013) 69:1361–1395
123
Garcı´a-Guinea J, Lombardero M, Roberts B, Taboada J, Peto A (1998)
Mineralogy and microstructure of roofing slate: thermo-optical
behaviour and fissility. Materiales de Construccio´n 48(251)
Gayko G, Cholcha W, Kietzmann M (2000) Anti-inflammatory,
antibacterial and antimycotic effects of dark sulfonated shale oil
(ichthammol). Berl Munch Tierarztl Wochenschr 113(10):368–
373
Hockmann A, Kessler DW (1950) Thermal and moisture expansion
studies of some domestic granites. US Bur Stand J Res
44:395–410
Ivaldi G, Catti M, Ferraris G (1988) Crystal structure at 25 and 700 C
of magnesiochloritoid from a high-pressure assemblage (Monte
Rosa). Amer Mineral 73:358-364
Jackson JA (1997) Glossary of geology (4th edn). American
Geophysical Institute, Alexandria, VA
Klopfer H (1985) Feuchte. In: Lutz P, Jenisch R, Klopefer H (eds)
Lehrbuch der Bauphysik. Teubner, Stuttgart
Koch A, Siegesmund S (2004) The combined effect of moisture and
temperature on the anomalous behavior of marbles. Environ
Geol 46(3–4):350–363
Laborato´rio Nacional de Energia e Geologia, Portugal. http://e-geo.
ineti.pt/bds/ornabase/. Last accessed March 2012
Listemann H, Scho¨lermann A, Meigel W (1993) Antifungal activity
of sulfonated shale oils. Arzneimittelforschung 43(7):784–788
Midot D (1984) Etude ge´ologique et diagnostique me´talloge´nique
pour l0 exploration du secteur Minas (Uruguay). Tesis, 3eme
Cycle, Univ. P. et M. Curie, Parı´s, France, pp 1–175
Monicard RP (1980) Properties of reservoir rocks: core analysis.
Edition Technip, Paris
Montani C (2008) Stone. Repertorio economico mondiale World
marketing handbook Faenza Editrice. ISBN: 978-88-8138-121
Morales Demarco M, Oyhantc¸abal P, Stein KJ, Siegesmund S (2011)
Black dimensional stones: geology, technical properties and
deposit characterization of the dolerites from Uruguay. Environ
Earth Sci 63(7–8):1879–1909. doi:10.1007/s12665-010-0827-5
Special Issue: Monuments under Threat: Environmental Impact,
Preservation Strategies and Natural Stone Resources
Mosch S (2008) Optimierung der Exploration, Gewinnung und
Materialcharakterisierung von Naturwerksteinen. Dissertation,
University of Go¨ttingen
Mosch S, Siegesmund S (2007) Statischer Verhalten petrophysikali-
scher und technischer Eigenschaften von Naturwerksteinen. Z dt
Ges Geowiss 158(4):821–868
Natursteinwerk Theuma AG. http://www.natursteinwerk-theuma.de.
Last access March 2012
Oyhantc¸abal P, Spoturno J, Goso E, Heimann A, Bergalli L (2001)
Asociaciones litolo´gicas en las supracrustales del grupo Lava-
lleja y sus intrusiones asociadas en la hoja Fuente del Puma (Sur
de Minas). In: III Cong. Uruguayo de Geologı´a y XI Cong.
Latinoam. Geol. Montevideo, Uruguay. CD Abstract, 246
Oyhantc¸abal P, Siegesmund S, Stein KJ, Spoturno J (2007) Dimen-
sional stones in Uruguay: situation and perspectives. Z dt Ges
Geowiss 158(3):417–428
Oyhantc¸abal P, Siegesmund S, Wemmer K (2011) The Rı´o de la Plata
Craton: a review of units, boundaries, ages and isotopic signature.
Int J Earth Sci 100(2–3):201–220. doi:10.1007/s00531-010-0580-8
Passchier CW, Trouw RAJ (1996) Microtectonics, 2nd edn. Springer,
Berlin. ISBN 3-540-58713-6
Porada H (1989) Pan-African rifting and orogenesis in Southern to
Equatorial Africa and Eastern Brazil. Precambrian Res 44:103–136
Preciozzi F, Masquelin H, Basei MAS (1999) The Namaqua/
Grenville Terrane of eastern Uruguay. In: II South American
Symposium on Isotope Geology, Carlos Paz
Reeder RJ, Markgraf SA (1986) High-temperature crystal chemistry
of dolomite. Am Mineral 71:795–804
Robertson S (1999) BGS rock classification scheme, volume 2.
Classification of metamorphic rocks. British Geological Survey
Research Reports, Research Report 99-02
Robie RA, Bethke PM (1966) X-ray crystallographic data, molar
volumes and densities of minerals. Clark Jr SP (ed) Handbook of
physical constants. Geol Soc Am, pp 58–73
Ru¨drich J, Kirchner D, Siegesmund S (2011) Physical weathering of
building stones induced by freeze-thaw action: a laboratory long-
term study. Environ Earth Sci. 63:1573–1586. doi:10.1007/
s12665-010-0826-6
Ruiz Garcı´a C (1977) Aplicaciones al microscopio en relacio´n con la
calidad de las pizarras de techar. Boletı´n Geolo´gico y Minero.
T. LXXXVIII-I, pp 72–77
Sa´nchez Bettucci L (1998) Evolucio´n tecto´nica del Cinturo´n Dom
Feliciano en la regio´n Minas-Piria´polis, Uruguay. PhD Tesis,
Facultad de Ciencias Exactas y Naturales, Universidad de
Buenos Aires, pp 1–344
Sa´nchez Bettucci L, Ramos VA (1999) Aspectos geolo´gicos de las
rocas metavolca´nicas y metasedimentarias del Grupo Lavalleja,
sudeste de Uruguay. Rev Bras Geocienc 29:557–570
Sa´nchez Bettucci L, Peel E, Oyhantc¸abal P (2010) Precambrian
Geotectonic units of the Rı´o de La Plata craton. Intern Geol Rev
32(1):50–78
Shelley D (1993) Igneous and metamorphic rocks under the
microscope. Chapman and Hall, London
Siegesmund S, Du¨rrast H (2011) Physical and mechanical properties
of rocks. In: Siegesmund S, Snethlage R (eds) Stone in
architecture: properties, durability, 4th edn. Springer, Berlin
Siegesmund S, Stein KJ (2007) 150 Jahre Schiefer aus Lotharheil:
Kein Auslaufmodell. Naturstein 12:60–63
Strohmeyer D (2003) Gefu¨geabha¨ngigkeit technischer Gesteinsei-
genschaften. Dissertation, University of Go¨ttingen
Wagner W (2007) Grundlagen fu¨r die Pru¨fung von Dach- und
Wandschiefern. Z dt Ges Geowiss 158(4):785–805
Ward CR, Go´mez Ferna´ndez F (2003) Quantitative mineralogical
analysis of Spanish roofing slates using the Rietveld method and
X-ray powder diffraction data. Eur J Mineral 15(6):1051–1062
Weiss T, Siegesmund S, Kirchner D, Sippel J (2004) Insolation
weathering and hygric dilatation: two competitive factors in
stone degradation. Environ Geol 46:402–413
Environ Earth Sci (2013) 69:1361–1395 1395
123