SPECIAL ISSUE
Black dimensional stones: geology, technical properties
and deposit characterization of the dolerites from Uruguay
Manuela Morales Demarco • Pedro Oyhantc¸abal •
Karl-Jochen Stein • Siegfried Siegesmund
Received: 12 August 2010 / Accepted: 29 October 2010 / Published online: 7 December 2010
 The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Dimensional stones with a black color occupy a
prominent place on the international market. Uruguayan
dolerite dikes of andesitic and andesitic–basaltic compo-
sition are mined for commercial blocks of black dimen-
sional stones. A total of 16 dikes of both compositions were
studied and samples collected for geochemical and petro-
graphical analysis. Color measurements were performed on
different black dimensional stones in order to compare
them with the Uruguayan dolerites. Samples of the two
commercial varieties (Absolute Black and Moderate Black)
were obtained for petrophysical analysis (e.g. density,
porosity, uniaxial compressive strength, tensile strength,
etc.). Detailed structural analyses were performed in sev-
eral quarries. Geochemistry and petrography determines
the intensity of the black color. The Uruguayan dolerite
Absolute Black is the darkest black dimensional stone
analyzed in this study. The petrophysical properties of
Uruguayan dolerites make them one of the highest quality
black dimensional stones. Structural analyses show that
five joint sets have been recognized: two sub-vertical
joints, one horizontal and two diagonal. These joint sets are
one of the most important factors that control the deposits,
since they control the block size distribution and the
amount of waste material.
Keywords Dolerites  Black dimensional stones 
Petrophysical properties  Structural analysis 
Block size distribution  Uruguay
Introduction
Black dimensional stones are known on the international
market as ‘‘black granites’’ because their hardness and
strength are similar to those shown by granitic rocks.
Petrologically, these rocks are classified as gabbros,
norites, diorites, dolerites (or its synonym: diabase),
basalts and anorthosites. Five of them are considered
mafic rocks, except for anorthosite, which is classified as
a felsic rock.
The Uruguayan Dolerite Dike Swarm, which intruded
the Rı´o de la Plata Craton at 1,790 ± 5 Ma (Halls et al.
2001) is composed of hundreds of parallel dikes with an
average width of 30 m and average lengths of around
1,000 m. In Uruguay, they have been quarried since the
early 1960s due to their deep black color, which is always
en vogue, and their excellent technical properties, such
as extremely high uniaxial compressive strength (UCS)
and remarkable low porosity and water uptake. These
dimensional stones are used as high-quality cladding,
worktops, bathroom vanities, tombstones and precision
tables.
Due to their physical properties and appearance, these
rocks have been quarried since the time of ancient Egypt,
where they were used for the construction of sacred mon-
uments (tombs and temples) or magnificent buildings
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
Department of Geology, Faculty of Sciences,
Universidad de la Repu´blica, Igua´ 4225,
Montevideo 11400, Uruguay
K.-J. Stein
Natursteininformationsbu¨ro, Am Schulzensee 3,
OT Waldsee, 17258 Feldberger Seenlandschaft, Germany
123
Environ Earth Sci (2011) 63:1879–1909
DOI 10.1007/s12665-010-0827-5
(palaces) (Ashurst and Dimes 1998). They were also uti-
lized for the production of various decorative elements,
such as valuable pieces of art (e.g. statues, fountains, etc.).
Over the centuries and even today, dolerites and other
black dimensional stones are used for representative
buildings and other constructions worldwide.
Examples of the use of black dimensional stones in
Germany can be found in the Du¨sseldorf Airport, which
uses the Shanxi Black (dolerite) from northern China for
the interior flooring tiles. The Office of the Federal Presi-
dent in Berlin uses the Impala Dark (gabbro/norite) for the
building fac¸ade (Bo¨rner and Hill 2010) (Fig. 1a) and in
Bad Homburg the footbridge masts are constructed of Nero
Assoluto (gabbro) from Zimbabwe (Fig. 2). In the United
States of America, the base fac¸ade of the Empire State
Building utilizes Ebony Black (dolerite) from Sweden
(Ashurst and Dimes 1998) (Fig 1b) and in Uruguay the
entrance columns of the Antel Tower are made of Uruguayan
Black Absolute dolerite.
The prices for black dimensional stones on the inter-
national market vary from 900 to 2,400 US$/m3, whereas
the Uruguayan dolerites are priced at 900 to 1,700 US$/m3.
Dolerites from China have prices ranging from 1,000 to
2,000 US$/m3, the South African gabbro/norite shows
prices up to 2,000 US$/m3 and the most expensive black
stone is the iridescent norite from India with a price of
2,400 US$/m3. Prices depend on two aspects: the intensity
of the black color (the darker the stone, the more expensive
Fig. 2 Footbridge in Bad Homburg (Germany) made of Nero Assoluto from Zimbabwe (Source SBP GmbH). a General view of the footbridge;
b detail of support mast
Fig. 1 a Empire State Building (New York, USA) fac¸ade made of Ebony Black from Sweden. b Office of the Federal President in Berlin
(Germany) made of Impala Dark from South Africa
1880 Environ Earth Sci (2011) 63:1879–1909
123
it is) and the block size (the largest blocks are relatively
more expensive).
Present mining situation
In Uruguay, the methods of mining dolerites have evolved
since the 1960s when quarrying began. Mining was ini-
tially done by manual extraction and then evolved by using
the modern technique of the diamond wire saw, which has
proven to be a highly effective method.
The different periods in the production of dolerite blocks
are closely related to specific economic cycles in Uruguay
(Fig. 3). Since the beginning of production in 1960 and
until the end of the 1970s it was a period of slow growth,
with a maximal annual production of around 1,000 tons.
This first growth period was probably favored by the initial
support that the mining and geological sector received from
the military dictatorship during the period from 1973 to
1985. By the end of the 1970s, the government imple-
mented a macroeconomic deflation plan via a pre-
announced decrease of the exchange rate. Thus, Uruguayan
products became more expensive than they really were and
in the long run the exporters lost their competitiveness.
This situation lasted until 1982, when the country was in
the middle of a deep crisis. The government stopped bol-
stering the Uruguayan peso to the US dollar, leading to a
strong devaluation of the national currency. In these years
dolerite production suffered a sharp decline, of almost 90%
in the deepest moment of the crisis with respect to that of
the year 1978, which had the highest level of production on
record.
Later, the production entered into a new phase of growth
until the beginning of the 1990s, which was related to
regional/national growth cycles and the entry of new
investors in the stone sector. A new period of stagnation in
dolerite production occured at the beginning of the 1990s,
when the national economy entered into a new recession
phase. In the years 2001–2002, this period of recession turns
into a severe crisis, accompanied with a new devaluation of
the national currency. Dolerite production reached the
lowest level in the last 10 years, but as the economy
recovers so does the production of black dimensional stone.
Today production is in a new growth phase, mostly
influenced by the positive market trend for ‘‘Absolute
Black’’, which as of 2005 is due to the demand for stones
of black color. Despite the facts that in the present only
three companies are quarrying the dolerite dikes, the pro-
duction in the last several years has exceeded the average
of the last 45 years (Fig. 3). This can be directly related to
the use of the diamond wire saw, which increases the
efficiency of the extraction, and the recent trade policy
strategy that promotes the export of these products.
Historically, there have been 19 quarries, 4 of which
mined only superficial blocks. The quarries now active are
distributed in two regions in the Department of Colonia,
Fig. 3 Evolution of dolerite
production in Uruguay (Data
after Bossi and Campal 1991;
Morales Pe´rez 2004 and
Direccio´n Nacional de Minerı´a
y Geologı´a, DINAMIGE 2010)
and GDP (Gross Domestic
Product) in constant local
currency units (LCU) (Data
after World Bank homepage,
2010)
Environ Earth Sci (2011) 63:1879–1909 1881
123
one in the region of Arroyo de la Quinta, and the other in
the region of Polonia-Pichinango (see Fig. 4). Two quarries
are located in the same dike. Two large active sawmills are
in operation in the region, which cut the blocks extracted
from the quarries, produce polished slabs and sell the
products on the national and international markets. One
sawmill is located in Nueva Palmira with access to a har-
bor. The other sawmill is located in Las Piedras, 25 km
away from the main harbor in Montevideo (Uruguay). Both
harbors have the facilities to ship the blocks and other
processed materials, such as polished slabs. Numerous
small sawmills in the country buy the already polished
slabs.
The non-metallic mineral export of Uruguay in the year 2007
was around 4.4% of the total export of the country. No infor-
mation on the amount of dimensional stone exports is available.
In the last 10 years, the dimensional stone sector in
Uruguay has been represented by the production of granite
and syenite (red, pink, gray and dark green), slate (black,
gray, red and green), dolerite (black and dark gray), marble
(white) and recently sandstone (orange and yellow) (Fig. 5).
Granite and syenite production (plotted together in Fig. 5)
has decreased in the last 10 years as dolerite production has
grown. Marble production is marginal and sandstone has
entered the market in 2003 with its production continuing to
grow. Slate production has remained more or less constant
in the last 10 years. The strong decrease in the production of
granite and syenite reflects the growing predominance of
China as an exporter of these products.
The production of dimensional stones in the year 2004
represents around 0.26% of the non-metallic mineral pro-
duction (in tons). The dolerite production for the same year
is about 22% of the total dimensional stone production (in
tons). In US dollars, the dolerite production is almost 40%
of the total dimensional stone production (DINAMIGE
2010). This makes dolerite the most important dimensional
stone product of Uruguay.
The world demand for black dimensional stones of high
quality is not yet totally covered by the other productive
countries, such as China, South Africa, Sweden, Zimba-
bwe, India and Brazil. Uruguay, whose production is not
very large at the present time, will probably occupy a more
constant position on the world market when more dolerite
dikes are developed for production.
Fig. 4 Satellite image showing different dolerite dikes in the region
of Polonia-Pichinango along with active and inactive quarries (Image
Source Google Earth, 2010)
Fig. 5 Dimensional stone
production in tons (Data after
Direccio´n Nacional de Minerı´a
y Geologı´a, DINAMIGE 2010).
Data for granites and syenites
are combined
1882 Environ Earth Sci (2011) 63:1879–1909
123
Geological setting of the dolerite dike swarm
in Uruguay
The geology of Uruguay is characterized by a Precambrian
basement that crops out in the south part of the country.
This basement was originally divided into two regions by
Ferrando and Fernandez (1971), taking into account their
ages: the eastern domain belonging to the Brasiliano Cycle
(Neoproterozoic) and the western to the Transamazonian
Cycle (Paleoproterozoic).
The Rı´o de la Plata Craton was defined by Almeida
(1971) including the Transamazonian outcrops of southern
Brazil, Uruguay and Argentina. Fragoso-Cesar (1980)
defined the Dom Feliciano Mobile Belt of southern Brazil
and Uruguay, as a series of petrotectonic associations of
Brasiliano age.
Bossi and Ferrando (2001) divided the Uruguayan
basement into three tectonostratigraphic terranes: the Pie-
dra Alta and the Nico Pe´rez Terrane (these two terranes
correspond to the Rı´o de la Plata Craton) and the Cuchilla
Dionisio (corresponding to the Dom Feliciano Mobile
Belt). These terranes are separated from west to east, by
two first-order tectonic regional discontinuities: Sarandi del
Yı´ and Sierra Ballena Shear Zones (Fig. 6).
Recently, Oyhantc¸abal et al. (2010) proposed a redefi-
nition of the Rı´o de la Plata Craton, based on new and
previously published geochronological and isotopic data
that shows different events of crustal growth and crystal-
lization ages for the Piedra Alta and Nico Pe´rez Terrane.
These differences support the exclusion of the Nico Pe´rez
Terrane from the Rı´o de Plata Craton, which now com-
prises the Piedra Alta Terrane in Uruguay and the Tandilia
Belt in Argentina.
The Piedra Alta Terrane is especially significant for this
work because it contains the dolerite dike swarm.
According to Oyhantc¸abal et al. (2007a, b), this terrane is
composed of two supracrustal metamorphic belts with an
E–W direction. Each one of them is composed of a meta-
morphic volcanic-sedimentary formation and spatially
associated plutonic bodies, and extended granitic–gneissic
belts in between (Bossi and Ferrando 2001).
The metamorphic belts are from north to south: the
Arroyo Grande Belt and the San Jose´ Belt. The first one
was defined by Bossi and Ferrando (2001) and corresponds
to the Arroyo Grande Formation (a folded volcano-sedi-
mentary succession of greenschist facies, Oyhantc¸abal
et al. 2010) and associated intrusions formerly defined by
Ferrando and Fernandez (1971). The San Jose´ Belt com-
prises the Paso Severino Formation and associated intru-
sions, the San Jose´ Formation and the Montevideo
Formation (Oyhantc¸abal et al. 2007b). The Paso Severino
Formation, as defined by Oyhantc¸abal et al. 2010 consists
of a greenschist facies folded volcano-sedimentary
succession. The San Jose´ Formation is composed of par-
agneisses and garnet and staurolite-bearing micaschists
(Oyhantc¸abal et al. 2003, 2007a, b). The Montevideo
Formation comprises amphibolites, paragneisses and gar-
net and staurolite-bearing micaschists (Bossi 1965; Bossi
et al. 1993; Oyhantc¸abal et al. 2003, 2007a, b).
Between these belts there are elongated granitic–gneis-
sic areas that also include decameter to kilometer-sized
blocks of micaschists, paragneisses and amphibolites.
These areas are known as the Florida Central Granitic–
Gneiss Belt (Bossi and Ferrando 2001; Oyhantc¸abal et al.
2010).
The tectono-thermal activity of this terrane, and therefore
the Rı´o de la Plata Craton, consists of two Transamazonian
events at 2.2–2.1 and 2.1–2.05 Ga (Oyhantc¸abal et al. 2010).
An orogenic event occurs with the intrusion of the basic
dike swarm in an extensional regime (Bossi and Ferrando
2001) at 1,790 ± 5 Ma (U–Pb on baddeleyite by Halls
et al. 2001). This swarm encompasses an area of 25,000
km2 (100 km width and 250 km length) with a general
trend of ca. 060 and intrudes in all the lithologies of the
Florida Central Granitic–Gneiss Belt (Bossi and Campal
1991). This mafic dike swarm (Bossi et al. 1993) is also
known as the Uruguayan Dike Swarm (Teixeira et al. 1999;
Fig. 6 Schematic geological map of Uruguay (modified from Hart-
mann et al. 2001)
Environ Earth Sci (2011) 63:1879–1909 1883
123
Halls et al. 2001) or the Florida Dyke Swarm (Mazuchelli et al.
1995).
The craton was stable for a long time after the intrusion
of the basic dike swarm, until the last event at the end of
the Proterozoic, when its edge was reworked by a dextral
mega-shear known as the Sarandı´ del Yı´ Shear Zone. This
event caused the rotation of the eastern extreme of the dike
swarm to the south (Bossi and Campal 1991).
Characterization of the dolerite deposits
In Uruguay, a wide spectrum of names are used to describe
these rocks. They have been called ‘‘black granites’’
(mostly in the commercial sector; Bossi and Navarro 1982;
Bossi et al. 1990; Techera et al. 2004; Comunita` Econo-
mica Europea-Uruguay, no date), microgabbros (Bossi and
Navarro 1982; Bossi et al. 1989; Bossi and Campal 1991;
Bossi and Ferrando 2001; Spoturno et al. 2004), andesitic
and andesitic–basaltic dikes (Bossi and Campal 1991;
Bossi et al. 1993, Bossi and Ferrando 2001), gabbros
(Comunita` Economica Europea-Uruguay, no date) and in
the recent literature dolerites (Oyhantc¸abal et al. 2006,
2007a, b, 2008).
The term dolerite, synonymous with diabase and
microgabbro, is used to describe an igneous hypabyssal
rock of dark color composed of plagioclase (labradorite
in composition) and clinopyroxene (normally augite or
titanoaugite), with opaques as the main accessory minerals
(magnetite, titanomagnetite or ilmenite). The grain size is
between that of gabbro and basalt (medium-grained,
between 1 and 5 mm) and the typical texture is ophitic or
subophitic (laths of plagioclase totally or partially sur-
rounded by crystals of augite) (Allaby and Allaby 1990;
Jackson 1997).
Bossi and Campal (1991) studied and related the pet-
rographic characteristics to the geochemical features,
dividing the dike swarm into two groups. One group
comprises rocks of andesitic composition and high titanium
content (Group A) and the other one of andesitic–basaltic
composition and low titanium content (Group B). In the
present work these two groups were also recognized.
In each dike it is possible to recognize three zones when
taking into account the grain size (see Figs. 7, 8; Table 1).
Figure 9 depicts the distribution of the different zones.
Zone 1 is in contact with the country rock; its thickness is
not more than 60 cm, is normally very finely fractured and
defines the chilled margin of the dike. Zone 2 is 1–1.5 m
thick, is less fractured and characterized by a fine grain that
increases toward the middle of the dike. Zone 3 is located
in the center of the dike, representing ca. 90% of the width.
The contact with Zone 2 is gradual. The grain size in this
zone is medium-grained, ranging from 1 to 2 mm.
In the three quarries where a grain size profile was taken
and analyzed, observations indicate that Zones 1 and 2 on
both sides of the dike represent not more than 11% of the
dike width (Fig. 7). As shown in Table 1, no strong cor-
relation between the dike width and the maximal grain size
exists, although the wider dikes (for example U8 and U59)
show the coarser grain and the finer dikes (as the case of
U62) show the finer grain. Further investigations are still
necessary to clarify this observation.
Geochemistry
Major and minor elements were determined by X-ray
fluorescence spectrometry at the GeoForschungsZentrum in
Potsdam (Germany). A total of 24 samples from 14 dikes
were already investigated by Bossi et al. (1993) and a total
of 28 samples from 16 dikes were analyzed in this study.
Another five dikes were identified, but they were unreach-
able for samples collection. In some dikes two samples were
analyzed, one from Zone 2 (fine-grained) and the other
from Zone 3 (medium-grained), in order to ascertain the
Fig. 7 Grain size distribution in
three dolerite quarries. High
TiO2: U8, Rosarito and U11,
Blackstone; Low TiO2: U66,
Pimafox (grain size of
phenocrysts and groundmass
separated)
1884 Environ Earth Sci (2011) 63:1879–1909
123
geochemical differences that can be correlated to the
petrography of these rocks.
The results of these analyses (Tables 2, 3) corroborate
the observations made by Bossi and Campal (1991), who
divided the dikes into two groups based on their geo-
chemistry that correspond to the two petrographic groups.
Group A is characterized by relatively high contents of
TiO2 (between 1.5 and 2.5%) and an andesitic composition,
and Group B is defined by relatively low contents of TiO2
(\1.2%) and an andesitic–basaltic composition. This is
shown in the De La Roche diagram in Fig. 10. Group A
also shows relatively higher values for the other major
elements: FeOt, MnO, Na2O, K2O, P2O5, but lower values
of Al2O3, MgO and CaO (Fig. 11). They also exhibit dif-
ferent mg# values (MgO/MgO ? FeOt), where the values
for Group A are around 0.17 and 0.25 and those for Group
B are between 0.35 and 0.45.
Group B shows higher values of the following trace
elements: Rb, Ni, Y, Zn and V and lower values of Cr with
respect to Group A. The other trace elements, Nb, Zr, Sr,
Ba and Ga, show a similar distribution between both
groups.
In both groups, a different geochemical signature in the
two dike zones considered can be recognized. Regarding
the major elements, Zone 2 represents an enrichment of the
following elements in Groups A and B: TiO2, Na2O, K2O
Table 1 Dike width and grain
sizes in Zones 2 and 3
Group Sample Quarry/Location Grain size (mm) Dike width (m)
Zone 2 Zone 3
Group A (high TiO2) U215 La Sierra 0.68 16
U62 Las Acacias 0.40 1.00 19
U12B Talita Chica 1.70 20
U12A Talita Grande 1.70 25
U55 Mexico 0.60 1.30 30
U56 Los Fresnos 1.70 30
U64 Pintado 0.44 1.70 35
U11 Blackstone 0.80 1.50 38
U59 Omar Mendez 0.65 2.00 40
U8 Rosarito 0.45 1.80 41
Group B (low TiO2) U199 Arroyo Polonia 0.60 20
U66 Pimafox 0.76 1.65 24
U61 Inex S.A. 0.20 25
U13 Victor 0.40 1.50 30
U58 Boria 0.50 30
U243 Arroyo de la Quinta 1.75 30
Fig. 8 Grain sizes in Zones 2
and 3 for both dike groups
Environ Earth Sci (2011) 63:1879–1909 1885
123
and P2O5, and a decrease of SiO2, MgO and CaO. For some
other major elements a different behavior can be observed.
In Group A, an enrichment of FeOt and MnO and a
decrease in Al2O3 is observable, when comparing Zone 2
to Zone 3. In the Group B, the opposite behavior occurs.
Trace elements are distributed as follows: there is an
enrichment of Rb, Nb, Zr and Ba in Zone 3 of both dike
groups, whereas only Group A presents an enrichment of
Sr and Ga in this zone. Cr, Ni and Zn behave differently
between both groups, where enrichment occurs in Zone 2
of Group A and a decrease is observable in the same zone
of Group B. Y and V also show a different behavior
between both groups, with an enrichment of these elements
in Zone 2 of Group B, and a decrease in Group A. Different
geochemical signatures between both groups can be
explained by various stages in the magmatic evolution
within a tholeiitic series, with Group A being more evolved
than Group B (Fig. 12).
Petrography
Bossi and Campal (1991) described the petrography of the
dike swarm based on the differences correlated with the
two geochemical groups in the dikes. According to these
authors, the main petrographical differences between both
groups are mineralogical, where the high TiO2 rocks
Fig. 9 Black Stone Quarry in
dike of Group A.
a Schematically figure where
Zones 1, 2 and 3 (Z1, Z2 and
Z3, respectively) are
represented; b general view of
quarry, contact with country
rock is shown; c contact zone of
dike with the country rock.
Strongly fractured chill margin
(Zone 1), not fractured Zone 2;
d Zone 3, with few horizontal
and vertical joints
1886 Environ Earth Sci (2011) 63:1879–1909
123
(Group A) show lower plagioclase contents. The plagioclase
is of andesine composition in Group A and in low TiO2 rocks
(Group B) plagioclase shows labradoritic composition.
The clinopyroxene present in both groups is augite, but
in Group B orthopyroxene (broncite) can also occur. Bossi
et al. (1993) determined the composition of the clinopy-
roxenes as augite to subcalcic augite and pigeonite with
high Ca contents. In Group A, more opaques occur con-
sisting of magnetite and ilmenite intergrowths, which are
normally automorph crystals associated with pyroxene.
Only small proportions of pyrite and chalcopyrite are
present. In Group B, the most important opaque mineral is
skeletal ilmenite, which is associated with quartz–feldspar
intergrowths and sometimes with pyroxene. Amphibole is
present as a product of uralitization of clinopyroxene and is
more common in Group A.
The term ‘‘micropegmatite’’ is used to refer to quartz
intergrowths, normally composed of quartz and alkali
feldspar, but sometimes also composed of quartz and pla-
gioclase. These intergrowths are much more abundant in
Group A, where they are composed of quartz and oligo-
clase. When apatite occurs, it is always related to these
intergrowths. According to Bossi and Campal (1991), the
grain size between 0.1 and 0.2 mm of the plagioclase laths
characterizes the ‘‘Granito Negro Absoluto (Fig. 13a).
‘‘Granito Negro Fino’’ (0.3 and 0.5 mm), ‘‘Granito Negro
Oriental’’ (0.6 and 0.8 mm) (Fig. 13b) and ‘‘Granito Negro
Grueso’’ (plagioclase laths [ 1 mm) all show larger grain
sizes.
Spoturno et al. (2004) have also studied these rocks, but
did not differentiate them into two groups. They described
the rocks as being composed of plagioclase with grain sizes
around 0.3 mm, when measured parallel to the long axis
(approximate composition: labradorite) and pyroxene, i.e.,
augite, pigeonite and occasionally orthopyroxene. Occa-
sionally, microphenocrysts of plagioclase and augite have
Table 2 Major element compositions of the dolerites (in wt.%)
Sample SiO2 TiO2 Al2O3 FeOt MnO MgO CaO Na2O K2O P2O5 Fe2O3 FeO H2O CO2 mg#
Group A
U8Z2 54.2 2.409 12.3 13.56 0.162 2.73 6.79 2.60 1.86 0.276 1.71 12.02 1.12 0.25 0.17
U8Z3 53.2 2.261 12.0 14.37 0.185 3.18 7.25 2.49 1.59 0.238 1.81 12.73 0.92 0.19 0.18
U11AZ2 55.4 1.733 12.9 12.54 0.173 3.04 6.97 2.58 1.75 0.224 1.58 11.11 0.63 0.13 0.20
U110Z3 53.2 2.332 12.2 14.50 0.184 3.07 7.25 2.56 1.64 0.247 1.82 12.85 0.59 0.09 0.17
U11Z2 54.1 2.269 12.2 13.53 0.171 2.94 6.99 2.58 1.74 0.255 1.70 11.99 1.10 0.19 0.18
U11Z3 53.2 2.243 12.0 14.35 0.184 3.22 7.26 2.50 1.61 0.238 1.80 12.71 0.89 0.19 0.18
U12AZ3 51.1 2.278 12.2 14.90 0.197 3.77 7.83 2.49 1.45 0.291 1.87 13.20 0.95 0.26 0.20
U12BZ3 51.2 2.297 12.3 14.96 0.196 3.77 7.81 2.50 1.46 0.288 1.88 13.25 0.86 0.22 0.20
U55Z2 50.2 2.419 12.9 14.10 0.205 4.26 8.22 2.56 1.51 0.369 1.77 12.50 0.95 0.24 0.23
U55Z3 53.6 2.192 11.7 14.20 0.184 3.11 7.11 2.49 1.62 0.262 1.79 12.58 1.08 0.32 0.18
U56Z3 53.1 2.251 11.9 14.48 0.186 3.19 7.22 2.53 1.63 0.240 1.82 12.83 0.88 0.20 0.18
U59Z3 49.4 2.380 13.0 14.32 0.212 4.81 8.63 2.46 1.37 0.343 1.80 12.69 0.80 0.25 0.25
U62Z2 55.1 1.750 12.7 12.77 0.173 2.99 6.92 2.55 1.76 0.224 1.61 11.31 0.78 0.13 0.19
U62Z3 55.2 1.782 12.7 12.83 0.175 2.98 6.93 2.57 1.78 0.223 1.61 11.36 0.74 0.21 0.19
U64Z2 53.4 2.300 12.1 14.27 0.184 2.99 7.06 2.57 1.69 0.322 1.80 12.65 0.81 0.19 0.17
U64M2 52.4 2.190 12.3 14.37 0.193 3.51 7.64 2.50 1.48 0.254 1.81 12.73 0.76 0.24 0.20
U215Z2 55.4 1.761 12.8 12.40 0.162 2.95 6.69 2.57 1.82 0.226 1.56 10.99 1.13 0.13 0.19
U215Z3 55.6 1.786 12.9 12.36 0.163 2.92 6.70 2.57 1.84 0.226 1.55 10.95 1.12 0.14 0.19
Group B
U13Z2 52.2 0.844 15.5 8.81 0.151 5.94 8.68 2.18 1.83 0.115 0.97 7.93 2.18 0.17 0.40
U13Z3 53.2 0.812 14.9 9.24 0.149 6.68 9.62 1.94 0.98 0.109 1.02 8.32 0.79 0.34 0.42
U58Z2 53.7 0.912 14.4 10.07 0.157 5.60 9.34 2.08 1.14 0.121 1.11 9.07 0.86 0.20 0.36
U58Z3 53.8 0.873 14.2 10.00 0.158 5.67 9.32 2.04 1.08 0.116 1.10 9.00 1.16 0.33 0.36
U61Z2 53.9 0.929 14.5 9.94 0.150 5.44 9.34 2.09 1.17 0.123 1.09 8.94 0.89 0.17 0.35
U66Z2 53.9 0.789 14.7 9.07 0.146 6.48 9.56 1.94 0.96 0.106 1.00 8.17 0.99 0.17 0.42
U66Z3 53.2 0.737 15.0 8.82 0.145 7.13 9.74 1.87 0.91 0.099 0.97 7.94 0.82 0.29 0.45
U199Z2 53.4 0.826 15.1 9.16 0.150 6.47 9.34 1.94 1.04 0.113 1.01 8.25 1.04 0.17 0.41
U243Z3 53.5 0.808 15.2 9.05 0.141 6.42 9.42 1.94 1.04 0.112 0.99 8.14 1.13 0.09 0.42
Environ Earth Sci (2011) 63:1879–1909 1887
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been observed with sizes up to 2 mm giving the rock a
microporphiritic texture. Accessories include ilmenite with
leucoxene rims and apatite. These authors also described
the presence of amphibole of uralitic origin, a product of
alteration of pyroxene.
The petrographical observations corroborate the previ-
ous research, with new information being added by this
study. In Table 4 the main observations are summarized
and the petrographic details are shown in Figs. 14, 15, 16,
17 and 18.
Using the Michel–Levy method, the plagioclase laths in
Group A were determined to have an An34–An44 composi-
tion (andesine), whereas Group B shows an An47–An60
composition (labradorite). In both groups, plagioclase occurs
as fine-grained euhedrally zoned laths (for grain sizes see
Table 1; Figs. 7, 8). In Group A, the laths commonly contain
inclusions of very fine-grained apatite crystals.
The clinopyroxene is generally augite, but also some
pigeonite can be observed. The augite in Group A occurs as
small crystals with grain sizes between 0.4 and 0.6 mm.
They are euhedral to subhedral, very often exhibit twining
and are surrounded by amphibole and to a lesser extent by
biotite. In Group B, the augites are coarser grained, with
sizes ranging between 0.4 and 2.4 mm. The crystals are
euhedral to subhedral and generally show an aspect ratio up
to four. Very often they show twining and are sometimes
surrounded by amphibole and biotite.
Biotite is present as euhedral to subhedral crystals with
sizes up to 0.9 mm (with an aspect ratio of 4.5) in Group A.
In Group B, the grain size only reaches 0.2 mm with an
aspect ratio of 2. In both groups it occurs as an accessory.
The biotite present is always related to magnetite or augite.
All samples exhibit the presence of granophyric inter-
growth as described by Shelley (1993), which Bossi and
Campal (1991) and Spoturno et al. (2004) refer to as
‘‘micropegmatite’’ or interstitial quartz–feldspar inter-
growths. In some cases, microcline can be recognized
within the granophyric intergrowth, but in other thin sec-
tions it is difficult to determine the nature of the feldspar
present. They are normally up to 0.8 mm in size in Group
A, but up to 1.6 mm in some cases and smaller in Group B,
up to 0.6 mm.
Opaques are also present as accessory minerals and are
much more frequent in Group A, where magnetite crystals
are euhedral to anhedral and the ilmenite crystals are
skeletal. Both crystals always occur with augite and biotite
as intergrowths, never surrounded by plagioclase. Their
size is between 0.2 and 0.8 mm. In Group B, the opaques
are skeletal, long and lath-shaped ilmenite up to 0.7 mm
with an aspect ratio up to 14. The very fine-grained mag-
netite crystals are subhedral to anhedral with a size up to
0.3 mm. Both are often distributed around augite as well as
around the plagioclase. The opaques are homogeneously
distributed in the grain size zones (1, 2 and 3), and in Zones
1 and 2 their grain size is generally smaller than the pla-
gioclase laths. In Group B, the opaques are sometimes
surrounded by red spots of limonite or hematite.
Apatite is found as an accessory, as very small (up to
0.1 mm in length) euhedral crystals with basal hexagonal
sections and needle-like longitudinal sections. They are
always included in the granophyric intergrowth and can be
very often found as inclusions in the plagioclase of Group A.
Hornblende occurs as a product of uralitization of
clinopyroxenes, where they appear either with fibrous habit
or as euhedral to subhedral crystals with sizes up to
0.4 mm. They are more frequent in Group A.
Calcite occurs only as an accessory in a dike from Group
B in Zone 3 (sample U13). It appears as very fine-grained
(up to 0.2 mm) anhedral to subhedral crystals normally
associated with biotite.
The texture normally observed in both groups is subo-
phitic, but there are some local variations. A porphyritic
Table 3 Trace element compositions of the dolerites (in ppm)
Sample Cr Ni Rb Nb Zr Y Sr Ba Zn Ga V
Group A
U8Z2 136 107 24 8 115 20 194 386 76 16 211
U8Z3 22 29 39 10 203 37 198 478 128 22 328
U11AZ2 54 31 52 11 212 37 207 485 115 20 381
U110Z3 25 25 47 10 195 34 211 453 132 21 404
U11Z2 41 44 35 10 180 34 195 403 124 20 437
U11Z3 54 33 50 10 215 36 214 482 118 21 373
U12AZ3 135 103 15 6 112 20 189 270 74 20 206
U12BZ3 175 115 16 6 106 16 187 275 72 16 201
U55Z2 140 109 30 7 115 22 195 355 80 19 208
U55Z3 77 106 21 4 126 22 212 661 84 18 222
U56Z3 49 30 44 13 204 36 214 483 118 19 368
U59Z3 54 32 49 12 224 37 235 817 98 21 398
U62Z2 28 33 45 10 192 32 199 463 125 20 404
U62Z3 82 107 25 6 125 24 196 307 85 18 220
U64Z2 51 30 47 12 209 39 283 1,732 102 21 385
U64M2 100 63 33 11 244 44 146 339 147 21 377
U215Z2 28 31 33 6 194 33 201 447 127 20 440
U215Z3 81 111 33 7 116 21 193 283 84 19 227
Group B
U13Z2 32 47 30 10 194 40 176 409 130 21 440
U13Z3 25 31 41 10 193 36 200 451 125 22 411
U58Z2 147 110 18 8 111 17 191 282 77 16 203
U58Z3 139 109 66 6 119 18 235 528 52 18 213
U61Z2 81 54 37 13 267 46 155 373 136 20 348
U66Z2 26 27 45 9 187 35 205 451 127 21 414
U66Z3 22 20 52 12 211 39 214 516 121 22 323
U199Z2 30 49 33 8 192 35 174 393 129 20 429
U243Z3 25 25 43 11 206 34 253 1,117 118 19 392
1888 Environ Earth Sci (2011) 63:1879–1909
123
Fig. 10 Distribution of the
dikes in a R1–R2 diagram (after
De La Roche et al. 1980)
Fig. 11 Box plots of major elements in Groups A (High TiO2) and B (Low TiO2) (in wt.%) by taking into account the grain size. Group A is blue
and Group B is red. Bold line median; box Q1–Q3 range; whiskers standard deviation above and below the mean of the data; filled circles outliers
Environ Earth Sci (2011) 63:1879–1909 1889
123
texture is observed in the chilled margins of two dikes from
Group B and in one from Group A. In the dike from Group
A the phenocrysts are plagioclase (sample U55) and in the
dikes from Group B they are plagioclase and augite. In one
sample (U13) they are altered to calcite and chlorite,
respectively.
In both dolerite groups the normative mineral compo-
sitions show more or less comparable values (see Table 5).
The M value (color index: total volume percent of mafic
minerals) varies between 29 and 37% in Group A and
between 31 and 34% in Group B.
For both groups the normative M values are comparable
between Zones 2 and 3. For Group A, Zone 2 has a value of
31 and Zone 3 a value of 33%. In Group B, both zones have
an M value of 33%. Only one sample of Group A shows an
important difference: 37% in Zone 2 and 33% in Zone 3
(Quarry U55). Although, M values for zones 2 and 3 are
comparable, the Absolute Black (Zone 2) appears much
darker than the Moderate Black (Zone 3) due to the smaller
grain size.
This color index, which is determined by the nor-
mative mineral composition, shows some differences
compared to the modal mineral composition. In Group
A, the modal mineral composition exhibits a M value of
49% in Zone 2 and 38% in Zone 3. Group B shows 49%
in Zone 2 and 47% in Zone 3. All the samples have an
M value higher than 30%, and therefore are classified as
mesocratic.
Determination of commercial varieties: influence
of grain size, fabric, chemical and mineral composition
A first classification based on the color of the rock and
grain size of plagioclase was made by Bossi and Campal
(1991) and continued by Bossi and Schipilov (2007). They
determined that the Absolute Black is aphanitic with a
mean grain size between 0.1 and 0.2 mm. Fine Black is a
fine-grained variety with a grain size between 0.3 and
0.5 mm. Normal Black (known as Oriental) has a grain size
between 0.6 and 0.8 mm and the Coarse Black is coarser
than 1 mm.
The results and observations collected in the current
investigation broadly agree with the above classification.
However, a new one is proposed based on variations in
grain size, measured on the c axes of the plagioclase laths
that are slightly different, and therefore the Uruguayan
dolerites can be classified as follows: Absolute Black
(Negro Absoluto), with aphanitic texture, grain size
\1 mm, Moderate Black (Negro Oriental) with phaneritic
texture, 1–2 mm and Special Black, which is similar to
moderated black but with some heterogeneity in the color,
for example: green or white spots due to the presence of
large hornblende and plagioclase crystals, respectively.
The chemical composition influences the mineralogy,
and therefore the de´cor of the rock. For both groups, rocks
of Zone 2 are darker than those of Zone 3, caused by higher
modal M values, but also by their smaller grain size, as the
mafic minerals are better distributed in the whole rock.
Fig. 12 AFM diagram showing the distribution of the dikes
Fig. 13 a Absolute Black dolerite; b Moderate Black dolerite
1890 Environ Earth Sci (2011) 63:1879–1909
123
Color measurements
Color measurements were performed at the Labor fu¨r
Baudenkmalpflege in Naumburg (Germany) on 12 different
black dimensional stones. In Fig. 19, all results are listed.
The L* values ranged from 25.22 for the Absolute Black
dolerite to 42.47 for the Kvemo quartz–phyllite. a* values
are between -0.03 for the Impala gabbro/norite and 1.00
for the Galaxy Brazil. b* values range between -0.13 for
Kvemo and 1.60 for Impala (Fig. 19).
Motoki and Zucco (2005) developed a classification that
takes into account the B parameter (brightness) from the
HSB color system (see Appendix). The category limits
determined by these authors have been converted to the
CIE Lab color system as follows: black (L \ 27), dark gray
(27 \ L \ 58), light gray (58 \ L \ 87) and white
(L [ 87). Utilizing this classification, the Absolute Black
dolerite can be defined as black and the Moderate Black
dolerite as dark gray.
Occurrences and deposits
Regional distribution: length, width, frequency, country
rock relations
The two groups investigated from the dike swarm intruded
into an area of 20,000 km2 and in all the lithologies of the
Piedra Alta Terrane, which consists of granites, metagra-
nites and metasediments (Fig. 20). Bossi et al. (1993)
pointed out that Group A crops out more often in the
northern part of the Piedra Alta Terrane and Group B more
to the southern part.
The dikes and the quarrying were first mentioned in
Bossi (1969). All the mining concessions and 15 locations
where the dikes were mined were mentioned in an internal
report of the DINAMIGE (National Geological Survey of
Uruguay; Medina and Carrio´n 1986). In 1987, Medina and
Carrio´n presented another report that described just the
dikes affected by exploration and the mining permissions
obtain from the Florida Department.
Bossi et al. (1989) presented the first photogeological
map where the distribution of the dikes is shown. The
map depicts thousands of parallel dikes intruding the
‘‘ancient orogenic cycle’’ or what it is now known as the
Piedra Alta Terrane (PAT). The dikes follow a NE–E
direction, but in the eastern margin of the terrane, near
the Sarandı´ del Yı´ Shear Zone, they change direction to
S–SE, due to the dextral shear activities during the Pro-
terozoic. They were recognized using aerial photographs
at 1:20,000 scale and corroborated with field observations
(Bossi and Campal 1991). Since this map is based on
photographic aerial surveys, it was impossible to verify
the presence of all these dikes in the field, and therefore
the number of dikes is probably smaller than originally
proposed.
Table 4 Petrographical data for Groups A and B
Geochemical classification Group A, high TiO2 content (between 1.5 and
2.5%) Andesi-basalt
Group B, low TiO2 content (less than 1.2%) Basalt
Plagioclase Between An34 and An44. Up to 40%, no
significant differences between both zones
Between An47 and An60. Up to 48% in Zone 2 and 44%
in Zone 3
Clinopyroxene Mostly augite, some pigeonite can be present, up
to 25%, no significant differences between both
zones
Mostly augite, some pigeonite can occur, up to 40%, no
significant differences between both zones
Granophyric intergrowth Around 10% in Zone 2 and 20% in Zone 3 Around 2% in Zone 2 and 10% in Zone 3
Amphibole Hornblende as uralitization product of
clinopyroxene, up to 13% in Zone 2 and 7% in
Zone 3
Hornblende as uralitization product of clinopyroxene,
up to 4% in Zone 2 and 6% in Zone 3
Opaques Magnetite in euhedral to subhedral crystals,
ilmenite in skeletal crystals, up to 8%, no
significant differences between both zones
Ilmenite in elongated crystals, up to 2%
Apatite Always present in granophyric intergrowth and
as inclusions in PI
Always present in granophyric intergrowth and as
inclusions in PI
Biotite As accessory associated with clinopyroxenes and
opaques
As accessory associated with clinopyroxenes and
opaques
Texture Subophitic, occasionally porphyritic in Zone 1
and 2, phenocrystals of PI and Aug
Subophitic, frequently porphyritic in Zone 1 and 2,
phenocrystals of PI and Aug
Grain size (Pg) Between 0.5 and 1 mm in Zone 2, and between 1
and 2 mm in Zone 3
Between 0.5 and 1 mm in Zone 2, and between 1.5 and
2 mm in Zone 4
Mineral abbreviation after Kretz (1983): An anorite, Aug augite, PI plagioclase
Environ Earth Sci (2011) 63:1879–1909 1891
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More recently, Spoturno et al. (2004) published a geo-
logical and mineral resources map for the San Jose´
Department at a scale of 1:100,000. This represents an area
of almost 5,000 km2, which corresponds to approximately
the half of the area to where the Piedra Alta Terrane crops
out. They recognized a total of 11 dikes; 6 of them have
been mined in the past for the extraction of dolerite blocks
for the dimensional stone market. Techera et al. (2004)
studied in detail the different quarries present in the San
Jose´ Department and their observations are in accordance
with those of Bossi and Campal (1991) and Bossi and
Ferrando (2001).
The field observations made in the current investigation
support most of the conclusions of the previously men-
tioned authors. They are:
1. The dikes are parallel to each other and strike ENE.
The length of each dike is usually greater than
1,000 m. In the area of Polonia-Pichinango four
quarries are located within the same dike (Fig. 4).
Some dikes may have a greater extension as is
presently assumed.
2. According to Bossi and Campal (1991), the widths of
the dikes range from 0.5 to 80 m, being in average
Fig. 14 General overview of
the Uruguayan dolerite fabrics.
a and b Zone 2 in dike from
Group A. c and d Zone 3 in dike
from Group A. e and f Zone 2 in
dike from Group B. g and
h Zone 3 in dike from Group B
(Left column plane polarized
light; right column crossed
polarized light)
1892 Environ Earth Sci (2011) 63:1879–1909
123
20 m. In this investigation the width of the dikes,
where a quarry is located, were determined to be
between 19 and 41 m.
3. The contacts with the country rock are usually plane
and parallel, sub-vertical and dip steeply toward the
southeast.
Fig. 15 Texture and mineralogy of Zone 3 in dike from Group A.
a Biotite crystals surrounding magnetite–ilmenite and hornblende
crystals partially surrounding augite and magnetite–ilmenite crystals
(plane polarized light, width of view 1.8 mm). b Same image as in
(a), but in crossed polarized light. c Augite crystal almost totally
replaced by hornblende with inclusions of opaque minerals (plane
polarized light, width of view 0.45 mm). d Same image as in (c), but
in crossed polarized light
Fig. 16 a Skeletal ilmenite and euhedral magnetite, dike of Group A,
Zone 3 (plane polarized light, width of view 1.8 mm). b Laths of
plagioclase and granophyric intergrowth (same image as in (a), but in
crossed polarized light). c Skeletal, long and lath-shaped ilmenite.
Group B dike, Zone 3 (plane polarized light, width of view 1.8 mm).
d Laths of plagioclase and crystals of pigeonite with typically curved
fractures (same image as in (c), but in crossed polarized light)
Environ Earth Sci (2011) 63:1879–1909 1893
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4. The dikes crop out in different ways and not
all along their projected paths. Sometimes large
boulders crop out; similar to those of granitic
rocks (Fig. 21a). In numerous cases the dolerites
are poorly exposed and usually very fractured
(Fig. 21b).
Fig. 17 a Subophitic texture in dike of Group A, Zone 3 (plane
polarized light, width of view 3.6 mm). b Same image as in (a), but in
crossed polarized light. c Subophitic texture in dike of Group B, Zone
3 (plane polarized light, width of view 3.6 mm). d Same image as in
(c), but in crossed polarized light
Fig. 18 a Equigranular texture in dike of Group A, Zone 2, where a
homogenous distribution of the opaques are visible (plane polarized
light, width of view 3.6 mm). b Same image as in (a), but in crossed
polarized light. c Porphyritic texture in dike of Group B, Zone 2.
Several phenocrysts of plagioclase are visible (plane polarized light,
width of view 3.6 mm). d Same image as in (c), but in crossed
polarized light
1894 Environ Earth Sci (2011) 63:1879–1909
123
5. There is no preferred topographical outcrop posi-
tion. The dikes are found at the top and in the
middle of hills but also at the same contour level as
streams.
A summary of the dikes sampled are listed in Table 7.
Characterization of dolerite deposits: controlling
parameters
The main controlling parameters affecting the deposits of
dimensional stones are the volume of the deposit, the
Fig. 19 Color measurements
for various black dimensional
stones
Fig. 20 Geological map with sampled quarries (map redrawn after Bossi and Ferrando 2001)
Environ Earth Sci (2011) 63:1879–1909 1895
123
ensemble of lithological aspects (e.g. fabric, mineralogy,
geochemistry, etc.) and the tectonic inventory.
The volume is important because enough material has to be
present in order to furnish a steady product for regional or
international markets, and thus such an occurrence can be
considered as a suitable provider. The dolerite deposits are
characterized by their tabular shape, being a two-dimensional
deposit. The volume of the deposit is limited by the length of
the dike and its width, whereas the depth is determined by how
deep it is technologically possible to mine.
In Uruguayan deposits, the maximum depth that has been
reached in a dolerite quarry is around 10 m. Medina and
Carrio´n (1987) reported that in the quarries U12A and U12B
drillings were performed, but any report on the results is
lacking. This is also the case of drillings in the quarry U8,
where the drill cores are available, but the drilling location and
direction is unknown, so it is impossible to know the depth of
drilling. The maximum mining depth in this kind of deposit
has been attained in the dolerite quarries of Sweden, where the
extraction of blocks can reach up to 50 m.
The second controlling parameter is the ensemble of
lithological aspects that indicates if the rock is suitable as a
dimensional stone, since these influence the de´cor, e.g. the
color and fabric of the rock. For black dimensional stones,
the intensity and homogeneity of the black color is very
important, so that no other color spots are present. Excep-
tions to this assumption are the cases where such hetero-
geneities make an improvement in the quality of the de´cor,
e.g. the Star Galaxy from India or Black Galaxy from Brazil.
Tectonic elements are the third controlling parameter.
The main structural elements are joints, which are mainly
distributed as orthogonal sets and are probably the result of
the cooling and contraction of the rock.
In Fig. 22 the main joint sets are represented, which were
observed in all the investigated dikes. Previous authors
(e.g. Medina and Carrio´n 1986, 1987; Bossi and Campal,
1991) have also reported on these joint sets. Three main joint
sets occur, two sub-vertical and one horizontal. The two sub-
vertical sets are orthogonal: one parallel to the dike walls
striking 070–085 and dipping toward the NW or SE (repre-
sented as Vt 1 in Fig. 22), and the other one perpendicular to
the dike walls striking to 320–360 and dipping toward the NE
or SW (represented as Vt 2 in Fig. 22). The sub-horizontal
joint set shows dips up to 10 in all directions.
The distribution of the joints in several quarries has been
measured in order to calculate the potential block size that
can be extracted. The first two joint sets observed are
represented in the plots of Fig. 23. A meaningful difference
in the orientation of the joints cannot be observed between
the dikes of Groups A (High TiO2) and B (Low TiO2).
However, the dikes of Group A display a higher frequency
of joints parallel to the dike wall, whereas the dikes of Group
B show a higher frequency of joints perpendicular to the dike
wall and of joints that dip to the SW. Since these joint sets are
Fig. 21 a Large boulder of dolerite weathered in place. b Poorly exposed dolerite outcrop
Fig. 22 3D model of joint sets found in dolerite dikes. X direction:
dike width, Y direction: dike length, Z direction: depth. Hz horizontal,
Vt 1 vertical 1 (parallel to dike length), Vt 2 vertical 2 (perpendicular
to dike length), Dg 1 diagonal 1 (parallel to dike length) and Dg 2
diagonal 2 (perpendicular to dike length)
1896 Environ Earth Sci (2011) 63:1879–1909
123
orthogonal to each other, regular-sized blocks can be quar-
ried. If the spacing between the joints is large enough, the
quarry is able to produce blocks on a profitable basis. The
problem with this type of deposit is the existence of other
joint sets that crosscut the orthogonal ones. Diagonal joints
have also been previously described by Bossi and Campal
(1991) and Medina and Carrio´n (1986). Although these joints
are not very frequent, their significance for the quarrying
operation is very important as they crosscut the regular
blocks that could be extracted, increasing the proportion of
waste material and minimizing the production of marketable
blocks (Fig. 24). In statistical documentations they are often
overseen (Fig. 23). Diagonal joints have been isolated in the
plots of Fig. 25 in order to better visualize them.
The two diagonal sets are also orthogonal to the dike
direction and both have dips between 11 and 75. One
diagonal set strikes N070-085 and dips toward the NW or
SE (Dg 1 in Fig. 22), and the other one strikes N320-360
and dips to the NE or SW (Dg 2 in Fig. 22).
Quality assessment of dolerites deposits
All the dikes can be subdivided into three zones by
their grain size: Zone 1 (very fine-grained), Zone 2
(fine-grained) and Zone 3 (medium-grained). In quarries
located in the dikes of Group A, in which their Zone 2
is unfractured, field observations indicate that the
Absolute Black variety can be mined (e.g. Black Stone
Quarry, see Fig. 9). The Moderate Black variety (Negro
Oriental in Uruguay) is extracted from Zone 3. Since
Zones 1 and 2 are not more than 11% of the dike, the
ratio between Absolute Black and Moderate Black is at
best 0.124.
Several decades ago the scarcity of joints in a dimen-
sional stone deposit was a very negative aspect for the
extraction, because they could not be used to facilitate the
mining of the blocks (Bossi and Campal 1991). Today the
diamond wire saw makes it possible to cut a block of
dolerite without any previous discontinuity. However, the
problem of a greater proportion of joints in a quarry per-
sists, which is one of the controlling factors in the quar-
rying of dolerite deposits.
Characterization of the waste material
Before starting the extraction of any dimensional stone, the
weathered material (including rounded boulders) and sed-
imentary deposits that covers the fresh rock must be
Fig. 23 a Total joints measured. b Joints measured in Group A dikes. c Joints measured in Group B dikes. Stereograms: equal area, lower
hemisphere. Contours: 1, 2, 3, 4, 5 times uniform distribution
Fig. 24 a Diagonal joint dipping parallel to the dike walls and b diagonal joints dipping perpendicular to the dike walls
Environ Earth Sci (2011) 63:1879–1909 1897
123
removed. These materials are called overburden or simply
waste rock. In addition to these materials, an important
amount of country rock (no matter if fresh or weathered)
must also be extracted for safety reasons (instabilities, etc.)
while quarrying. Considering a mining depth of 50 m, a
width of 30 m and a dike dip angle of 89, the proportion
Table 5 Normative mineral distributions in both groups (in wt.%)
Group Sample Q Ort Ab An Hy Di Mag Ilm Ap Cc Percentage
of An in PI
Group A (high TiO2) U8M1 10.4 11.3 22.6 16.8 18.2 12.2 2.5 4.7 0.7 0.6 42.7
U8P7 8.9 9.7 21.7 17.3 19.9 14.3 2.7 4.4 0.6 0.5 44.4
U11A 10.9 10.6 22.3 19.0 18.6 11.9 2.3 3.4 0.5 0.3 45.9
U110 8.3 9.9 22.2 17.3 19.4 14.8 2.7 4.5 0.6 0.2 43.7
U11M1 10.0 10.6 22.5 17.2 18.5 13.3 2.5 4.4 0.6 0.4 43.3
U11M12 8.8 9.8 21.8 17.2 19.9 14.5 2.7 4.4 0.6 0.4 44.2
U12A 5.4 8.8 21.7 18.4 21.8 15.3 2.8 4.5 0.7 0.6 45.8
U12B 5.2 8.9 21.8 18.5 21.9 15.2 2.8 4.5 0.7 0.5 46.0
U55M1 3.0 9.2 22.3 19.9 21.6 15.2 2.7 4.7 0.9 0.6 47.2
U55M4 10.0 9.9 21.7 16.5 19.9 13.7 2.7 4.3 0.6 0.7 43.2
U56 8.5 9.9 22.0 16.7 19.9 14.7 2.7 4.4 0.6 0.5 43.1
U59 1.6 8.3 21.4 20.8 23.0 16.1 2.7 4.6 0.8 0.6 49.3
U62M3 10.8 10.7 22.2 18.6 18.8 12.2 2.4 3.4 0.5 0.3 45.6
U62M6 10.8 10.8 22.3 18.4 18.9 11.9 2.4 3.5 0.5 0.5 45.2
U64M1 9.1 10.3 22.4 16.9 19.6 13.4 2.7 4.5 0.8 0.5 43.0
U64M2 7.3 9.0 21.8 18.4 20.7 14.7 2.7 4.3 0.6 0.6 45.8
U215M1 11.4 11.1 22.4 18.6 18.6 11.2 2.3 3.4 0.6 0.3 45.4
U215M3 11.6 11.2 22.3 18.7 18.4 11.1 2.3 3.5 0.5 0.3 45.6
Average 8.4 10.0 22.1 18.1 19.9 13.6 2.6 4.2 0.6 0.5 45.0
Group B (low TiO2) U13M1 3.3 11.2 19.1 28.2 22.5 12.0 1.5 1.7 0.3 0.4 59.6
U13M10 6.3 5.9 16.7 29.6 24.1 13.3 1.5 1.6 0.3 0.8 63.9
U58M1 7.1 6.9 18.0 27.3 21.7 14.9 1.6 1.8 0.3 0.5 60.3
U58M3 7.9 6.5 17.7 26.9 22.1 14.5 1.6 1.7 0.3 0.8 60.4
U61 7.4 7.1 18.1 27.3 21.0 15.0 1.6 1.8 0.3 0.4 60.2
U66P1 7.4 5.8 16.8 29.1 22.8 14.4 1.5 1.5 0.3 0.4 63.4
U66P12 6.1 5.5 16.1 30.4 24.6 13.4 1.4 1.4 0.2 0.7 65.3
U199 6.7 6.3 16.8 30.0 23.7 12.7 1.5 1.6 0.3 0.4 64.2
U243 6.6 6.3 16.8 30.4 23.2 13.2 1.5 1.6 0.3 0.2 64.4
Average 6.5 6.8 17.3 28.8 22.9 13.7 1.5 1.6 0.3 0.5 62.4
Fig. 25 a Total diagonal joints measured. b Diagonal joints measured in Group A dikes. c Diagonal joints measured in Group B dikes.
Stereograms: equal area, lower hemisphere. Contours: 1, 2 3, 4, 5 times uniform distribution
1898 Environ Earth Sci (2011) 63:1879–1909
123
of waste rock to be removed is about 6.5% of the total
volume extracted and 26% when the dip is 70. However,
the amount of waste rock will significantly increase by
lower depths of exploitation as realize today in Uruguay
(maximum depth up to 10 m).
Another kind of waste rock produced comes from the
sections of the quarry where a high frequency of frac-
tures occurs. No production of profitable blocks can be
performed in these sections (Fig. 26). When the extracted
block, which differs from a rectangular cuboid, is squared
into one, new waste rock is produced that is highly
dependent on the joint systems. Internationally, the waste
material produced in dimensional stone quarries is around
30–50% of the extracted volume, however, in Uruguayan
dolerite quarries this value can reach up to 90% (Oyhantc¸abal
et al. 2007a, b).
Fig. 26 Comparison of two
sections of a dolerite dike:
a Section suitable for quarrying
dolerite blocks; b stereogram
showing joint distribution;
c diagram showing distances
between joints; d box plots
showing average distances
between joints and the minimal,
average and maximal block that
can be extracted; e section only
suitable for quarrying gravel;
f stereogram showing joint
distribution; g diagram showing
distances between joints and
h box plots showing average
distances between joints and the
minimal, average and maximal
block that can be extracted
Environ Earth Sci (2011) 63:1879–1909 1899
123
Petrophysical properties
The petrophysical investigations were carried out in the
laboratories of the Department of Structural Geology and
Geodynamics of the Geoscience Centre of the University
of Go¨ttingen, whereas the abrasion strength test (AST) was
conducted at the laboratories of AMPA (Amtliche
Materialpru¨fanstalt fu¨r das Bauwesen) of the University of
Kassel. The materials used for the petrophysical testing are
samples from Zone 2 and Zone 3 from the Black Stone
Quarry (U11), which is located in a dike from Group A. All
the results of the petrophysical properties are listed in
Table 6. Table 7 shows the main petrophysical properties
of other comparable black dimensional stones, such as
Table 6 Summary of the dikes sampled
Group Sample Quarry/Location Dike
width (m)
Present
condition
Quarry
depth (m)
Quarry/Outcrop
length (m)
Dike
length (m)
Strike
Group A (high TiO2) U8 Rosarito 41 In activity At least 8 100 3,500 N060
U11 Blackstone 38 In activity 8 140 500 N080
U12A Talita grande 25 Flooded At least 4 135 2,000 N075
U12B Talita chica 20 Flooded At least 3 150 2,000 N080
U55 Mexico 30 Flooded At least 6 135 1,500 N053
U56 Los Fresnos 30 Abandoned Superficial 170 3,400 N060
U59 Omar Mendez 40 Flooded At least 4 110 1,250 N070
U62 Las Acacias 19 Flooded 5 130 2,600 N072
U64 Pintado 35 Abandoned Superficial 430 430 N075
U215 La Sierra 16 No quarry – 220 500 N056
Group B (low TiO2) U13 Victor 30 Abandoned 8.5 110 1,900 N076
U58 Boria 30 Flooded At least 5 120 1,700 N076
U61 Inex 25 Flooded 11 225 2,400 N065
U66 Pimafox 24 In activity 4 60 2,000 N072
U199 Arroyo Polonia 20 No quarry – 55 560 N065
U243 Arroyo de la Quinta 30 No quarry – 120 800 N050
Table 7 Petrophysical properties of Group A (high TiO2)
Commercial name Negro Absoluto (Zone 2) Negro Oriental (Zone 3)
Rock type Dolerite Dolerite
Direction X Y Z X Y Z
UCS (MPa) 399.6 ± 33.6 371.4 ± 37.0 367.00 ± 16.2 266.2 ± 26.8 285.8 ± 29.2 274.7 ± 24.6
Young modulus (GPa) 32.90 ± 7.38 29.60 ± 9.90 30.59 ± 11.93 27.33 ± 15.77 23.47 ± 8.84 17.40 ± 4.54
Tensile strength (MPa) 16.7 ± 4.5 19.5 ± 4.3 17.4 ± 5.8 16.7 ± 3.0 15.9 ± 3.0 14.3 ± 3.4
Flexural strength (MPa) 51.8 ± 2.2 52.8 ± 2.1 46.1 ± 1.5 35.7 ± 2.5 30.8 ± 1.3 32.9 ± 1.3
Abrasion strength (cm3/50 cm2) 2.2 2.4 2.2 2.3 2.5 2.4
Breaking load at dowel hole (MPa) 4.7 ± 0.8 4.2 ± 0.7
Real density (g/cm3) 2.99 3.02
Apparent density (g/cm3) 2.99 3.02
Porosity (%) (vacuum) 0.03 0.06
Average pore radii (lm) 0.10 0.06
Most abundant pore radii class (lm) 0.01 0.02
Water uptake (%) (atmospheric) 0.01 0.02
Water uptake (%) (vacuum) 0.01 0.02
Vapor diffusion resistance factor 6,489 5,010
Thermal expansion (910-6 K-1) 6.63 6.60 6.53 6.54 6.56 6.90
1900 Environ Earth Sci (2011) 63:1879–1909
123
basic plutonic rocks or volcanic rocks. Future studies are
planned for determining the petrophysical properties in
samples from Group B.
Density, porosity and thermal expansion
Density values are similar to gabbro-dioritic rocks, to
which they can be compared. For the Absolute Black
variety the apparent density value is 2.98 g/cm3 and for the
Moderate Black the value is 3.02 g/cm3. In both varieties,
the real density is quite similar, 2.99 g/cm3 for Absolute
Black and 3.02 g/cm3 for Moderate Black. The density
values of some comparable rocks vary between 2.8 (for
Impala and Star Galaxy) and 3.3 g/cm3 (for Ebony Black)
(see Table 7).
The dolerites have very small values of porosity under
vacuum, around 0.03% for Absolute Black and 0.06% for
Moderate Black. Their pore radii distribution shows that
the most abundant pore radii class is 0.01 lm for Absolute
Black and 0.02 lm for Moderate Black, whereas the
average pore radii is 0.10 lm for Absolute Black and 0.06
for Moderate Black.
The vacuum and atmospheric water uptakes are very
low, 0.01 for Absolute Black and 0.02% for Moderate
Black due to the low porosity values. The values of the
comparable rocks in Table 7 vary between 0.05 and
0.33%, for Preto Absoluto and Shanxi Black, respec-
tively.
The thermal expansion differs between 6.53 9 10-6 K-1
for Absolute Black and 6.90 9 10-6 K-1 for Moderate
Black (Table 8). These values can be compared to those
determined by Hoffmann (2006) for a hornblendite
(6.64 9 10-6 K-1). There is no permanent change in length
after the heating/cooling-cycles.
Mechanical properties of black dimensional stones
The dolerite Absolute Black shows uniaxial compres-
sive strength (UCS) values that vary between 367.00
MPa in the z-direction and 399.56 MPa in the x-direc-
tion. Moderate Black shows lower values, with
266.22 MPa in the x-direction and 285.78 MPa in the
y-direction (for coordinates references see Appendix).
The UCS values for basic plutonic rocks range from
around 90 to 400 MPa (Mosch 2008) (Fig. 27a, b). The
Young0s modulus for Moderate Black was determined
to be 17.40 GPa in the z-direction and 27.33 GPa in the
x-direction, whereas for Absolute Black the values are
29.60 GPa in the y-direction and 32.90 GPa in the
x-direction.
The tensile strength values determined for the Uru-
guayan dolerites are between 16.68 MPa in the x-direction
and 19.49 MPa in the y-direction for the Absolute Black,
and between 14.31 MPa in the z-direction and 16.72 MPa
in the x-direction for the Moderate Black. According to
Mosch (2008), the tensile strength for basic plutonic rocks
is around 28 MPa.
The flexural strength values vary between 46.06 MPa in
the z-direction and 52.75 MPa in the y-direction for the
Absolute Black dolerite, and between 35.72 MPa in the
Table 8 Technical properties of comparable black dimensional stones (source Bo¨rner and Hill 2010)
Sample Origin Lithology Density
(kg/dm3)
UCS
(N/mm2)
Flexural
strength
(N/mm2)
Water
uptake
(vol.%)
Reference object
Shanxi Black
(G1401)
China Dolerite 3.0 350 0.33 Interior stone paving of
Du¨sseldorf Airport
Ebony Black Sweden Dolerite 3.1–3.3 294 25 0.10 Facade of Empire State
Building in New York
Impala South Africa Gabbro/Norit 2.8–3.0 221–260 22–26 0.08–0.32 Haus Sommer, Pariser Platz
1 in Berlin
Impala Dark South Africa Gabbro/Norit 3.0 290–300 0.10 Bundespra¨sidalamt in Berlin
Nero Assoluto Zimbabwe Fine-grained
Gabbro/Norit
3.0–3.1 240–252 24–29 0.12–0.16 Wallraf-Richartz- Museum in Koln;
Gramercy Plaza/Torrance
in California
Preto Absoluto Brazil Fine to middle-grained
basalt (Diabas) with
a touch of green
3.1 210 34 0.05
Star Galaxy India Fine to middle-grained
Gabbro/Norit
with bronzite scales
2.8–2.9 183–203 19–20 0.08–0.12
Absolute Black Uruguay Dolerite 3.0 367–400 46–53 0.01 Antel Tower in Montevideo
Moderate Black Uruguay Dolerite 3.0 266–286 31–36 0.02
Environ Earth Sci (2011) 63:1879–1909 1901
123
x-direction and 30.81 MPa in the y-direction for the Moderate
Black dolerite. The flexural strength values for basic plutonic
rocks are around 5–30 MPa (Mosch 2008) (Fig. 27c, d). The
breaking load at the dowel hole is 4.68 MPa for Absolute
Black and 4.21 MPa for Moderate Black.
The abrasion strength varies between 2.16 cm3/50 cm2
in the z-direction and 2.36 cm3/50 cm2 in the y-direction
for Absolute Black and 2.26 cm3/50 cm2 in the x-direction
and 2.53 cm3/50 cm2 in the y-direction for Moderate
Black. These are very low values considering the values
given by Hoffmann (2006) for diorite, between 7.5 cm3/
50 cm2 and 15 cm3/50 cm2, meaning that the Uruguayan
dolerites show a high resistance to material loss due to
abrasion.
Summary: evaluation of the ‘‘black stone’’ deposits
Quality assessment with respect to color and de´cor
Dolerites are valuable dimensional stones, mainly because
of two distinct properties: their black color and the possi-
bility of extracting them in larger blocks. The black color is
directly related to the de´cor, and therefore to three prop-
erties of the rock: the mineral composition, the texture
(which includes grain size, grain shape, and its interlocking
flow structures and the observed reaction textures) and the
structure (e.g. layering or inclusions). The latter two belong
to the rock fabric.
The minerals that determine the black color are mela-
nocratics, such as pyroxene, hornblende, opaques and
biotite. Changes in the color can be produced when leuc-
ocratic minerals are present or minerals resulting from
autohydrothermal reactions. Minerals, such as plagioclase,
alkali feldspar and quartz–feldspar intergrowths create
white spots in the rock. Green spots are developed when
hornblende is present.
The value of black stones increases when the minerals
are homogeneously distributed in the rock, exhibit no flow
textures, visible intergrowths, nor reaction textures or any
visible structure that alters the black color of the rock. If
melanocratic minerals are homogeneously distributed, then
the rock will have a homogenous color, which can be black
or gray depending on their proportion and on the grain size
of the rock. Rocks with a finer grain size and the same
percentage of melanocratic minerals tend to be darker.
Fig. 27 a UCS versus apparent density; b flexural strength versus apparent density; c UCS versus porosity and d flexural strength versus
porosity (modified after Mosch 2008)
1902 Environ Earth Sci (2011) 63:1879–1909
123
Layering in a black rock affects it negatively, as well as the
presence of veins of leucocratic minerals.
For all black dimensional stones three color qualities are
defined: absolute black, moderate black and special black.
The absolute black color in a dimensional stone can be
developed in three different cases. First, when the rock is
composed of 100% melanocratic minerals. Second, the
rock is composed of melanocratic and leucocratic minerals
and the latter contain inclusions of melanocratic minerals,
and when the grain size is extremely fine.
The moderate black color can be generated when the
melanocratic minerals make up 30–60% of the rock and the
grain size is coarse (up to 2 mm) making both mineral
colors distinguishable. Three special cases can arise which
affects the color of moderate black stones. The first can
occur in both varieties when there are minerals present that
interrupt the normal color of the stone. Two examples of
this are the presence of granophyric intergrowths that
produce white spots and the presence of broncite in gabbro
that produces golden spots (such as in the Star Galaxy
variety of India). Autohydrothermal alteration creates the
second special case where whole color changes are pro-
duced in the rock. This occurs by the process of uraliti-
zation that produces a slightly green coloration. The third
situation is given when the rock is cut by veins of different
color or layering is present that modifies the whole rock
color.
The color index of the Uruguayan dolerites calculated
using normative minerals varies between 31 and 33% in
Group A and is 33% in Group B. When the color index is
calculated using modal analysis, the values are higher.
Zone 2 in both groups shows higher modal M values than
Zone 3. Zone 3 of Group A shows lower M values (38%)
with respect to Group B (47%), and in both groups Zone 2
can have the same M value (49%). The rock is therefore
classified as mesocratic using both, the normative and the
modal M value.
Color variations are related to changes in the grain size,
which determines the quality of the main rock varieties. In
Uruguayan dolerites, the color of the Absolute Black
variety is until now only found in the dikes of Group A.
The most important characteristic of Absolute Black is the
very small grain size and its homogeneity. The porphyritic
texture observed in Zone 2 of some deposits drastically
reduces its quality.
The Moderate Black variety develops a dark gray color,
in both groups. This is due to the medium grain size of the
leucocratic and melanocratic minerals that are distin-
guishable without any optical aid.
Grain size variations are sometimes visible on the sides
of the extracted and squared blocks. A clear layering of
melanocratic and leucocratic minerals was not observed;
however, in three quarries (two classified as Group A and
one as Group B) the presence of leucocratic veins has been
observed.
Autohydrothermal alteration can have a negative influ-
ence on the color in some parts of a deposit, especially in
combination with a porphyritic texture as in Zone 2. When
the autohydrothermal alteration is homogenously distrib-
uted throughout the entire deposit the quality of the Mod-
erate Black variety is not negatively affected.
Granophyric intergrowths are visible as white spots
within a black background, when they are larger than
1 mm. These intergrowths affect the quality of the Abso-
lute Black more negatively than the Moderate Black vari-
ety, because the latter one already has coarse white spots
(the plagioclase laths) that are homogeneously distributed.
From the color measurement results it can be concluded
that Absolute Black dolerite is the darkest of the black
dimensional stones considered in this study, followed by
Shanxi Black, Yi and Dark Larvikite. The a* parameter
(see Apendix) for the samples analyzed is generally posi-
tive (in one sample negative) and very low, indicating that
there is a very small proportion of red color in these rocks.
The b* value is also generally positive (in one case nega-
tive) and very low, indicating that the rocks studied also
have a proportion of yellow in their color. The values a*
and b* for the samples considered are so small that they
have no influence on the color of the sample, which is
determined only by the L* value.
Utilizing the classification scheme of Motoki and Zucco
(2005), the rocks analyzed in this study are black and dark
gray. Absolute Black dolerite is black, as well as Shanxi,
Yi, Dark Larvikite and Brazil Black and Moderate Black
dolerite is dark gray, as well as the rest of the rocks
analyzed.
Petrophysical aspects
The application and use of dimensional stones are finally
controlled by the technical and petrophysical properties.
Under normal conditions in a building the technical
requirements of a dimensional stone are moderate. Extreme
applied loads are seldom. More often the dimensional
stones have to show high flexural strength and high resis-
tance to the climatic conditions or the chemical reactants to
which they can be exposed to.
In comparison to other black rocks on the international
market, the Uruguayan dolerites have similar or even better
physical (technical) properties. Particularly the Absolute
Black variety shows a maximal compressive strength of
400 MPa and a maximal flexural strength of around
50 MPa. With such high resistance values, these rocks can
be used safely in many building parts that require a high
compressive and flexural strength. Examples include
building fac¸ades, free-standing constructions in a building,
Environ Earth Sci (2011) 63:1879–1909 1903
123
such as floating stairs, columns and architraves or counter-
tops. The footbridge in Bad Homburg (Germany) is a very
good example of the use of this type of high strength rock,
where individual blocks of Nero Assoluto dolerite from
Zimbabwe are used as load-transferring masts.
The low porosity, water uptake, thermal expansion and
also the high abrasive resistance of the rock makes it an
appropriate material for counter-tops and precision tables
for technical/industrial purposes. These types of construc-
tions usually require a high quality, pertaining to their
physical, chemical and geometrical properties (e.g. length
measures changes, susceptibility to chemical reactions,
evenness of the surface, high strength, etc.).
Block sizes distribution and modeling
The dimensions of the preferred blocks are determined by
the industrial processes that follows the extraction. The
blocks are required to be rectangular cuboids (or right
rectangular prisms) without irregularities (such as veins or
joints) and with the specified dimensions required for
extractable raw blocks. These dimensions determine
whether the block is of minimum, optimal, maximal or
special size. The minimum block is determined by the
smallest piece that can be commercialized, which is a
gravestone. The optimal block must have the adequate
dimensions to be cut in a diamond gang saw. The available
transport condition possibilities determine the maximal
weight of a block and therefore the dimensions of the
maximal block. The special blocks are determined by the
demand. For example, precision tables for technical/
industrial purposes may require the blocks to have the
dimensions of 3 m long, 1 m wide and half a meter thick.
Uruguayan dolerites have a density of 3 t/m3 and the
maximum block weight cannot exceed 28 tons, because
this is the maximum weight that can be transported in
containers. The different block dimensions can be distin-
guished into: small ones (between 0.5 and 1 m3), medium
blocks (between 1 and 3.3 m3), large blocks (between 3.3
and 6.6 m3) and very large blocks (larger than 6.6 m3). The
maximum block must be smaller than 9 m3.
The Black Stone Quarry is a good example for illustrating
block production from a dolerite deposit in Uruguay. Between
the years 2005 and 2009, this quarry produced a total of
2,536 m3 as shown in the block size frequency diagram in
Fig. 28. Most of the block sizes produced is of the small
dimensions with 34% of the total production and the medium
dimension making up 44%. Large blocks represent 17%, the
maximum blocks and the very large blocks come to 2.8% of
the total production. The proportion of Absolute Black in
production is very low, being 1.8% for the production time
span considered, 0.5% belongs to the small blocks, 0.8% to the
medium and 0.5% to the large blocks.
Sections of three quarries were modeled using the pro-
gram 3D-Block Expert developed at the University of
Go¨ttingen (see Siegesmund et al. 2007a, b; Mosch 2008
and Mosch et al. 2010, for details). The raw block size
distribution for the models obtained is shown in Fig. 29.
For the Black Stone Quarry a section having the dimen-
sions (8 9 8 9 6 m) has been modeled (Fig. 30a, c, d) and
the block size distribution analyzed in order to determine its
potential yield. The resulting prism is cut into slabs of 1 m
each (Fig. 30b) and then a possible block distribution can be
proposed (Fig. 31). From inclined joints it is evident that the
block sizes do not match any minimum raw block volume,
which corresponds to a higher amount of waste (Fig. 31).
The deposits are characterized by their two-dimensional
shape and their limited width, where the extraction can
either develop along the length or with depth. The length of
one single dike can be up to 3,500 m, such as the dike of
the Polonia-Pichinango area, but normally they only attain
a length of 1,000 m. The depths of the dikes in the study
area are unknown, but in other parts of the world eco-
nomical mining in such deposits can reach 50 m. Nor-
mally, the dikes do not exceed a width of 40 m. The
economically more interesting ones are those wider than
15 m, because initial observations show that the thinner
dikes have a finer grain size and a greater proportion of
Absolute Black. The dip of the quarry walls can present a
problem for mining safety, especially when a certain depth
is reached. The joint sets determine the efficiency of the
quarry, because they control the block size and the amount
of waste rock that will be produced.
When planning a mine based on the geometry of the
deposit, the efficiency of the mining operation increases,
and thus the production yield. Using the program 3D-Block
Expert, the volume of blocks extracted in a sector of a
quarry taking can be predicted, when taking into account
the joint distribution and geometry.
Fig. 28 Production between 2005 and 2009 for the Black Stone
Quarry. Block size frequency distribution of the Group A quarry for
both color varieties (Source Personal communication with Black
Stone Quarry owner)
1904 Environ Earth Sci (2011) 63:1879–1909
123
Estimation of the dolerite resources
The total quantity of dolerite dikes in the Piedra Alta
Terrane is difficult to estimate. The available information
can be used to estimate a maximum and minimum amount
of extractable dolerites.
According to Bossi and Campal (1991), the number of
dikes is around 300 and their average length and width is 460
and 20 m, respectively. The minimum value is based on
observations published by Spoturno et al. (2004) for the San
Jose´ Department, where they found a total of 11 dikes in an
area of 2,500 km2. If a similar dike distribution is assumed for
the rest of the area where the dikes crop out, a total of 88 dikes
may exist. The current investigation indicates that there are
about 19 dolerite quarries, where four of them have been
superficially mined and five of them are still in operation.
Fig. 29 The raw block size
distribution modeled for the
three quarries investigated using
the 3D-Block Expert program
Fig. 30 a and b Section in the
Black Stone Quarry modeled
with 3D-Block Expert (x = 6,
y = 8 and z = 8 m) and
represented with Intel Array
Viewer. The different joint sets
can be seen as well as the cross-
cutting diagonal joints; c image
of quarry section modeled;
d image of quarry section
modeled with slabs (one meter
each) represented
Environ Earth Sci (2011) 63:1879–1909 1905
123
The geometry for this type of deposit is simplified to
that of a cuboid or parallelepiped, where the width of the
dike is ‘‘a’’, the length is ‘‘b’’ and the depth of the dike is
‘‘c’’. The volume can be calculated by V = abc. To cal-
culate the reserves of dolerites in the Piedra Alta Terrane,
an average dike is considered to have a width of 30 m, a
length of 150 m and a maximum exploitation depth of
50 m. The total volume of this average deposit is
225,000 m3. Considering that 19 productive dikes at dif-
ferent stages of mining have already been identified in
Uruguay, the volume of the reserve base is 4,275,000 m3.
The efficiency of extraction for commercial blocks is not
better than 10% (Oyhantc¸abal et al. 2007a, b) and that
20,310 m3 were already extracted (Bossi and Campal
1991; Morales Pe´rez 2004; DINAMIGE 2010), a volume of
probable reserves of at least 407,500 m3 can be suggested.
From this volume around 10% of the rock has the quality of
Absolute Black.
Comparable dolerite quarries to those in Uruguay can
be found in Sweden. At present there are seven quarries
in Sweden where each of them produces an average of
8,000 m3 of stone per year (Swedish Geological Survey
2009). In comparison to Sweden, the production in
Uruguay is very low. In the last several years the
production ranged from 4,000 to 5,000 m3/year for the
five active quarries in the country. This comparison
indicates the production in Uruguay can be increased
several times, provided that an adequate exploration
strategy is followed.
Acknowledgments We would like to thank Bad Homburg SBP
GmbH for the Bad Homburg footbridge photos, Dr. R. Sobott
(Labor fu¨r Baudenkmalpflege in Naumburg) for the color mea-
surements, Dipl.-Ing. Peter Machner for the abrasion measurements
in the laboratories of the AMPA (Amtliche Materialpru¨fanstalt fu¨r
das Bauwesen) of the University of Kassel, Dr. Rudolf Naumann for
the geochemical measurement in GFZ (GeoForschungsZentrum) in
Potsdam and Janousˇek V, Farrow CM, Erban V and Sˇmı´d J for the
utilization of the program GCDKit (GeoChemical Data ToolKIT)
for the plotting of geochemical data. In Uruguay thanks to MsC.
Nelson Noya, Pilar Posada, Ing. Jorge Spoturno and MsC. Juan
Ledesma for the comments and suggestions related to the eco-
nomical aspects of Uruguay. We also thank Dr. Jorge Bossi for his
comments, the companies Black Stone S.A. and Comercio Exterior
S.A.. Special thanks also go to the students and friends for their
help. M. Morales Demarco is grateful to DAAD long term fellow-
ship (A/07/98548).
Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
Fig. 31 Possible block size distribution for the Black Stone Quarry
section using 3D Block Expert (each slab is one meter thick). a First
slab from top to bottom of the block. b Second slab, etc. The black
zones seen in (d, f and g) represent waste material. i Pie diagrams
showing the yield of each model section
1906 Environ Earth Sci (2011) 63:1879–1909
123
Appendix
Petrophysical techniques
Color measurements
Color measurements were performed using a Konica Mi-
nolta Chroma Meter CR 300 with a xenon flash-lamp with
a measuring spot of 8 mm in diameter. The results are
expressed in L*a*b* as required by the International
Commission on Illumination (CIE: Commission Interna-
tionale de l0Eclairage), where L* is the brightness (0 is
black and 100 is white), a* is the green/red axis (-60 is
green and ?60 is red) and b* is the blue/yellow axis (-60
is blue and ?60 is yellow).
Density and porosity, mercury injection porosimetry
and water uptake
The standard parameters apparent density (qap), real den-
sity (qr) and effective porosity (U) were determined as
described in Hoffmann (2006) using the Archimedes
Principle and relating the masses of a sample in dry (md),
wet (mw) and under water (buoyancy) (mb) conditions in
accordance with the following equations:
qap ¼ md=mw  mb ð1Þ
qr ¼ md=md  mb ð2Þ
U ¼ mw  md=mw  mb ð3Þ
The pore size distribution was measured by applying the
Mercury Intrusion Porosimetry using a ‘‘Porosimeter 2000’’
from the Company Carlo Elba. The samples, cylinders of
10 mm diameter and 40 mm length, are placed in a cell where
a vacuum is generated and afterwards filled with mercury. The
mercury is then forced into the pores of the sample, by
applying pressure in a progressive way. Since the pressure at
which the mercury enters the pores is inversely proportional to
the pore size, this is easily calculated.
Water uptake was measured following the DIN EN
13755 in 65 mm length cubes under atmospheric pressure
and under vacuum pressure. Simplifying the first procedure
consists in drying the sample and registering its mass and
then placing it under water and waiting 48 h until the
sample is completely wet, measuring the mass. The second
procedure consists in evacuating the dry sample for 24 h,
registering its mass and then placing it in under water for
48 h and afterwards registering the mass again.
Expansion properties: thermal expansion
Thermal expansion was determined in cylindrical samples
of 15 mm diameter and 50 mm length in three spatial
directions (X, Y, Z) in a special device called dilatometer,
as described in Strohmeyer (2003). The samples to be
measured were placed in the dilatometer which has six
linear displacement transducers with an accuracy of 1 lm
and two resistance thermometers (one of which is inside a
dummy) with an accuracy of 1K. The samples were sub-
jected to temperature cycles beginning at 20 up to 90C
with a rate of increase of 1C/min, which ensures the
thermal equilibration of the sample (Weiss et al. 2004). The
thermal dilatation coefficient a is a measure of how much
the length of a sample varies with a change in temperature.
The following formula allows its calculation:
a ¼ Dl = l DTð Þ ð4Þ
where Dl is the length change, l the length of the sample at
the beginning of the measurement and DT the temperature
change in units of 10-6 K-1. Residual strain e is the ratio
between the change in the length of a sample Dl and its
original length for a defined temperature interval in units of
mm/m.
Mechanical properties
The mechanical tests were performed using a Universal
Testing Machine Class 1 from the company Walter & Bai.
For each test, samples were prepared in order to recognize
anisotropies, therefore they were drilled in three orthogonal
directions (see Strohmeyer 2003, Figs. 2-3 and 2-4).
The uniaxial compressive strength (UCS) test was per-
formed following the DIN EN 1926 in at least 6 samples,
having a diameter and length 50 mm. The method consists
in applying perpendicular to the faces (which are plan-
parallel polished until ±0.1 mm accuracy) a maximum
force up to 1,000 kN with a load increase of 1,000 Ns-1.
The UCS (rucs) is calculated by using this equation:
rucs ¼ F=A ð5Þ
where F is the maximum force at which the sample breaks
and A is the area in which this force is applied.
Young’s modulus (E) is determined in the UCS test and
is a measurement of how much a material resists being
deformed when a uniaxial force is applied to it. Therefore,
it relates the strength (r) applied and the strain (e) of this
material, following this equation:
E ¼ drucs=de ð6Þ
For the measurement of the tensile strength the norm
DIN 22024 was followed. A maximum force of 50 kN is
applied with a load increase of 30 Ns-1 onto cylinders of
40 mm diameter and 20 mm length, but in order to develop
a tensile strength this force is applied perpendicular to their
faces. The tensile strength (rT) is calculated by the
following equation:
Environ Earth Sci (2011) 63:1879–1909 1907
123
rT ¼ 2F=dlp ð7Þ
where F is the maximum force at which the sample is
crushed, d is the diameter and l the height of the sample.
Breaking load at the dowel hole was determined fol-
lowing the DIN EN 13364. Instead of using samples with a
200 mm edge length and 30 mm thickness, smaller sam-
ples were used (150 mm edge lengths and a thickness of
30 mm), which do not have significant difference in the
resistance value according to Koch (2005). This method
consists in applying a force (up to 50 kN) at a load increase
of 50 Ns-1 perpendicular to a dowel fixed in the side of the
sample and registering the maximum force at which it
breaks down.
The flexural strength under concentrated load is deter-
mined by the norm DIN EN 12372 in samples with
150 mm length, 50 mm width and 25 mm height. The
procedure consists in placing the sample over two sup-
porters with 125 mm distance between them. In the middle
of the sample a maximum linear force of 50 kN is applied
with a load increase of 50 Ns-1 until the rock failure. The
equation used to calculate the flexural strength is the
following:
rF ¼ 3Fd=2wh2 ð8Þ
where F is the maximum force at which the samples breaks
down, d is the distance between the supporters, w is the
sample width and h is its height.
Abrasive resistance was performed by the Bo¨hme
Method as described in the DIN 52108. A square sample
with side lengths of 71 mm (with a surface area of 50 cm2)
and a height of 25 mm is placed in a grinding path with
some pressure above it and an abrasive powder underneath
it. The grinding path rotates at a speed of 30 rmp and after
22 revolutions it stops. The sample is then rotated in 90
and another 22 revolutions are started. After the sample has
been rotated four times its weight is measured. This pro-
cedure is repeated another four times. The value of the
abrasive resistance is expressed in the volume lost per
50 cm2 of sample (DV50 cm2 ) and is calculated by the fol-
lowing equation:
DV50 cm2 ¼ Dm  50ð Þ= qrarð Þ ð9Þ
where Dm is the loss in mass, qr is the apparent density and
ar is the real area of the sample surface.
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