Roques anglès - Turisme Andorra la Vella

ANDORRA LA VELLA
ROCKS IN THE STREET
OPEN GEOLOGY MUSEUM
ROCK GARDEN
GEOLOGICAL ITINERARY
GRANITE ARCHITECTURE
ITINERARY
We don’t realise, but in our urban surroundings there
are hidden riches which can help us to know more
about the natural environment. We are inevitably
bound up with nature; she offers us all the resources
we need to carry out our daily life.
Without having to go to far places in the earth, we can
find in our urban surroundings that are an accessible
area, many varieties of sedimentary, magmatic and
metamorphic rocks and we can even find fossils of
great quality. Another factor is that some of the constructions are evidence of the use that we have historically made of the materials offered us by nature,
although this usually goes unnoticed.
The purpose of the Open Geology Museum “Rocks in
the Street” is to bring out the values of world geodiversity and the geological heritage of Andorra
through the observation and study of elements
belonging to our daily life; they have always been there
and we have seen them, but now we can learn to see
them in a different way. We invite you to take a stroll
through the streets of Andorra la Vella, finding the panels with their explanations, designed to introduce you
into the always interesting world of geology.
ROCK GARDEN
Located in the Parc Central, in this
“Garden” you can find examples of
the rocks which are found in
Andorra.
The Rock Garden is accompanied
by a series of panels which tell us
about rocks in general, rocks in
Andorra and their uses.
C/ B. Riberaygua
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Rock Garden
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Andorra la Vella
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Plaça
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GEOLOGICAL ITINERARY
You start in Plaça Príncep Benlloch
and continue through various
streets of the parish.
The itinerary has several stopping
places, always in front of a building. At each stop a panel asks you
to observe a detail of the rock
used in the building and gives
explanations related with geology.
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Prat
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Casa
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Plaça
Guillemó
C/ Doctor Nequi
Av. Príncep
Benlloch
C/
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C/ D
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Plaça
P. Benlloch
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C/ Mossèn
Cinto Verdaguer
Av. Meritxel
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Beginning of the itineraries
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B.
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C/ C
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C/ Joan
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Geological itinerary
Pça. de la
Rotonda
Pont
de París
Av. Mitjavila
Granite architecture itinerary
The museum that is in
Andorra la Vella is divided
into three parts:
GRANITE ARCHITECTURE
ITINERARY
You start near the Plaça Príncep
Benlloch and again continue
through various streets in the
capital.
This itinerary also has various
stops where you are shown buildings which belong to “granite
architecture”. At these stops, you
will see typical features of this
architectural current and its importance in the Andorran context. The
granite architecture itinerary has
been organised with the collaboration of the Inventory and
Conservation Area of the Ministry
of Foreign Affairs, Culture and
Cooperation.
THE ROCKS
ROCKS IN ANDORRA
Rocks are natural materials constituted of one or more types of
minerals. In nature we find three
types of rock: igneous or magmatic rock, sedimentary rock and
metamorphic rock.
THE SITUATION
Andorra is located in the geological
nucleus of the Pyrenees, in the socalled Pyrenean axial zone, where
the rocks are the oldest.
IGNEOUS
OR MAGMATIC ROCKS
There are by the cooling of molten
magma existing in the interior of
the Earth.
If the magma cools slowly, without
coming out through the surface, it
becomes rock with well formed
crystals, called plutonic rock,
which is the case of the granodiorites of Andorra. If the cooling is
quick, because the magma
emerges on the surface, volcanic
rock such as basalt is the result.
SEDIMENTARY ROCKS
These originate on the earth’s
surface or at the bottom of seas
or lakes, from deposited material
produced by the erosion of other
rocks; in this case they form
detritic rock, such as sandstones,
clays and conglomerates.
They may be also produced by
the chemical precipitation of substances dissolved in water, or the
accumulation of organic remains;
in this case they form calcareous
rocks such as limestones (pumice,
for example) or gypsum.
METAMORPHIC ROCKS
These are formed by subjecting
any kind of rock to high pressures
and/or temperatures but without
actually melting them. This
changes the initial mineralogy and
structure of the rock and produces
a new rock. Examples of these
rocks are slate, phyllite, schist and
gneiss. In general, the rocks in
Andorra are mostly metamorphosed.
AGE
Except for quaternary materials,
the rocks in Andorra are very old.
- The sedimentary materials
(except sediments left by glaciers)
are of an age contained probably
between 590 million years
(Precambrian) and 390-370 million
years (middle Devonian).
- It is considered that the gneiss
could be around 500 million years
old.
- The granodiorites are calculated
to have an age of 305 million
years.
Can you imagine these figures in
comparison with a person’s life
today?
COMPLEXITY
The rocks in Andorra have a
complex geological history when
we realise especially the fact that
they have suffered two orogenesis
processes (formation of a relief
through the lifting action of the
earth’s surface).
During the Carboniferous era, 300
million years ago, they experienced
the effects of hercynian orogenesis, which culminated in the formation of a folded mountain system,
subsequently eroded during the
Paleozoic era.
During the Tertiary era, the alpine
orogenesis took place which
formed the Pyrenees as we know
them today.
This long history means that the
rocks in Andorra show important
evidence of metamorphism.
THE TYPE
The rocks in Andorra can be divided generally into rocks of magmatic origin and rocks of sedimentary origin. Most, however, have
been subjected to metamorphism.
ROCKS ARE ALIVE
When we look at a rock, we
always have the impression that
it has been there “for ever”, that it
always has had the appearance
that we see and that it will stay
the same for “an eternity more”.
In fact, this is not true: constantly
and slowly, rocks change.
Each of the three types of rock
can turn into either of the other
two, or another rock of its own
type. This whole set of transformations is called “the rock cycle”.
Rocks of
magmatic origin
Rocks of
sedimentary origin
THE USE
OF THE ROCKS
Quartzite
Metamorphic rock of silica composition which comes from sedimentary rocks such as quartzarenite
and conglomerates.
Phyllite
Metamorphic rock, of low metamorphism, derived from clayey
sediments. It has a silky appearance and a foliated texture. It is
intermediate between slate and
schist.
ROCKS OF MAGMATIC ORIGIN
Granodiorite
Plutonic rock rich in silicon composed of quartz, feldspars, and
biotite mica.
Gneiss
Metamorphic rock which has been
subjected to strong compression
and high temperatures. It can be
of sedimentary or igneous origin. It
is composed of potassic feldspar
(forming large crystals), quartz and
biotite.
ROCKS OF SEDIMENTARY ORIGIN
Conglomerate
Large grain detritic sedimentary
rock, with more than 50% of the
components measuring over 2
mm. In Andorra many conglomerates are found in La Rabassa,
formed by pebbles of slate, quartz
and quartzite.
Limestone
Limestone rocks contain more
than 50% of calcium carbonate.
They are of very different origins,
chemical, biochemical and biological. They normally contain many
fossils.
Slate
Rock of sedimentary origin (detritic
with very fine grain) which has been
through a very low grade metamorphism. It has a matt appearance
and a foliated structure.
Schist
Metamorphic rock of low to medium grade, derived from sedimentary rocks such as lutites and, from
time to time, basic igneous rock
(poor in silicon). In Andorra, the
schists are included in the claypelite series.
Clay-pelite series
The clay-pelite series, in Andorra,
are alternations of different types of
rock very widespread throughout
the Principality: schists, quartzites,
conglomerates, sandstones, limestones, etc.
Each rock has its own physical
properties and components which
characterise it. It is precisely these
properties and elements that man
has taken advantage of in using
the rock. Here we see three examples of use, perhaps the most significant in Andorra.
ROMANESQUE
ARCHITECTURE
Let us look at a Romanesque
apse, such as that of the church of
Sant Esteve in Andorra la Vella.
The roof is tiled in slate (metamorphic rock) or, as they call it in
Andorra, of “llosa”. This use takes
advantage of the property of this
rock of breaking into thin slices,
known as foliation.
The walls are of granodiorite (plutonic rock), a very hard rock able
to withstand great pressure and
very resistant to weather conditions.
Finally, the window arches have
keystones of pumice (sedimentary
rock). Pumice is a very soft rock
and therefore easy to carve and
manipulate. As a result of this
property, this stone was much
used in the middle ages for sculpture.
THE CATALAN FORGE
In Andorra 32 mineralization sites
have been identified. The most
important are in Silurian slate, in
the form of iron minerals such as
hematite, goethite and pyrite.
The presence of iron in our rocks
enabled an important iron industry
to flourish between the 17th and
19th centuries: the called Catalan
forge.
If you would like to know more
about this, it is worth visiting the
Rossell Forge in La Massana and
following the itinerary “The Route
of the Iron” in the valley of Ordino.
GRANITE ARCHITECTURE
The beginning of the 1930s saw
the start in Andorra of an architectural current which lasted until the
1960s, characterised by the use of
granite ashlars to cover façades.
The granite was used in a very formal way and left visible for its lustre on the whole of the façade or
for some parts such as the corners
or openings.
This architecture, which meant a
radical break with the forms of
construction used in Andorra until
then, was influenced by Catalan
modernism through the architects
who came to work in Andorra,
such as Josep Puig i Cadafalch,
Celestí Gusi and Adolfo Florensa,
and also the Andorran Xavier Pla,
who was trained in Catalonia.
This architecture was also encouraged by the arrival of Spanish
stonemasons, particularly from
Galicia and Andalusia, experts in
the techniques of cutting granite.
The arrival of granite architecture
coincided with the beginning of the
tourist and hotel activity in
Andorra. We find that the first hotel
establishments in the Principality
are built in this style. The importance of this architecture comes
particularly from the fact that it was
undisputable evidence of the
processes of economic, social and
town planning transformation
which affected Andorra in the mid20th century.
ROCK GARDEN
GEOLOGICAL
ITINERARY
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Travertine
Travertine is a rock resulting from
the precipitation of calcium carbonate, often around stems,
branches and leaves, in river areas
or lakes, or around waterfalls.
Phyllite
Phyllite is a metamorphic rock, of
low metamorphism, derived from
clayey sediments. It has a silky
appearance and a foliated texture.
It is intermediate between slate
and schist.
Granodiorite
Granodiorite is a plutonic rock rich
in silicon, composed of quartz,
feldspars, and biotite mica.
Quartzite
Quartzite can be a metamorphic
rock of silica composition which
comes from sedimentary rocks
such as quartzarenite and conglomerates.
Gneiss
Gneiss is a metamorphic rock
which has been subjected to
strong compression and high temperatures. It can be of sedimentary
or igneous origin. It is composed
of potassic feldspar (forming large
crystals), quartz and biotite.
Conglomerate
Conglomerate is a detritic sedimentary rock, composed by
rounded grains measuring over 2
mm.
Limestone
Limestone rocks contain more
than 50% of calcium carbonate.
They are of very different origins,
chemical, biochemical and biological. They normally contain many
fossils.
Notice the folds of calcite that
there is in one of the blocks. These
are a consequence of the different
deformations that the rock has suffered.
Quartzitic sandstone
Limestone
Limestone rocks contain more
than 50% of calcium carbonate.
They are of very different origins,
chemical, biochemical and biological. They normally contain many
fossils.
Notice that this rock is formed of
tiny grains so small that you can
hardly see them with the naked
eye. Some shine (muscovite mica)
and others do not (quartz). This
rock is a quartzitic sandstone.
The formation of sandstones starts
from a parent rock which was broken up by the action of external
agents (rain, ice, wind...). Water
carries off the particles resulting
from the disaggregation and
deposits them in a certain place
forming a sediment. Later the sediment becomes compacted and
cemented and turns into this rock.
Schist
Schist is a metamorphic rock of
low to medium grade, derived from
sedimentary rocks such as lutites
and, from time to time, basic
igneous rock (poor in silicon).
Volcanic tuff
In Andorra there are few volcanic
rocks, the best place to observe
them is in the Communal Nature
Reserve of the Comapedrosa
Valleys. There, some rhyolitic tuffs
outcrop, composed by immersed
phenocrysts of quartz in a matrix
of quartz, plagioclase, chlorite and
muscovite.
Quartzite
Quartzite can be a metamorphic
rock of silica composition which
comes from sedimentary rocks
such as quartzarenite and conglomerates.
Slate
Slates are rocks of sedimentary
origin (detritics with very fine grain)
which have been through a very
low grade metamorphism. They
have a foliated structure.
In Andorra, the slates of Silurian
have been an object of exploitation
to obtain iron.
Slate
Slates are rocks of sedimentary
origin (detritics with very fine grain)
which have been through a very
low grade metamorphism. They
have a foliated structure.
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3
Nummulitic limestone
Gneiss
Notice that you cannot see very
much in this rock. Now, if you wet
it with a moist paper handkerchief
(there’s a fountain near), the rock
darkens and tiny circular white
forms appear. These are fossils
called nummulites.
Nummulites were single-celled
organisms which could be over 10
cm in diameter, with a calcareous
shell. They lived in the sea during
the Eocene era, around 40 million
years ago.
Notice the façade of the house
Casa Ferré street down (C/ de la
Vall nº 3). You will see large elongated white crystals (feldspars)
surrounded by smaller crystals, in
bands. This arrangement of minerals is called gneissic texture.
Gneiss is metamorphic rock
derived from granite or sedimentary rocks of the same composition
which have been very compressed
at high temperatures. During this
process the minerals of the parent
rock re-crystallise in a direction
generally perpendicular to the
compression applied, forming
bands.
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9
Schist
Fossiliferous limestone
Slate
Granodiorite
Notice the parts of this rock which
shine like silver. This is a mineral
called muscovite mica.
The schist that decorates this
façade is a metamorphic rock
derived from sedimentary rocks or
occasionally from basic magmatic
rocks, that is, poor in silicon.
Schist is formed inside the earth’s
crust by metamorphic processes
during which the minerals of the
parent rock, particularly micas, are
rearranged in planes. These have a
tendency to come apart in parallel
slices, more or less thick. This
property of the rock is called schistosity.
Notice this fine-grained limestone.
It has a high content of fossils
called brachiopods, embedded in
a matrix of calcite. These are fossils of marine bentonic invertebrates (that is, living on the sea
floor), their soft parts being
enclosed inside a shell formed of
two valves.
More than 30,000 species of brachiopods have been described, of
which now only 300 survive. The
age in which they were most
abundant was during the
Mesozoic, from 245 to 65 million
years ago.
Notice that this rock is stratified,
that it can manage to split in
slices. This property of slate of
breaking into slices is called foliation.
Slates come from fine-grain sedimentary rocks (such as clay) which
have been subjected to moderate
pressures and temperatures. This
process makes the minerals take
up stratified forms arranged in parallel. This orientation of the minerals gives place to foliation.
Notice the grains of this rock. We
can see basically that there are
three types: some black, some
opaque white and others translucent white. All of them are very
abundant. There are others of a
different appearance, but not so
abundant.
In a rock we speak of essential
minerals when referring to the
most abundant, the presence of
which is used as a method of classification. Accessory minerals are
those present in the rock in a
smaller proportion, less than 5%.
Accidental minerals are those
which are found only in certain
rock formations.
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Folds
Brick
Granodiorite
Glass
Notice the numerous folds in this
granite rock. You get the feeling
that the minerals have been fluid.
Although the rocks are hard, if we
subject it to high temperatures and
pressure they become ductile, but
without actually melting; it folds
without fracturing, as though it
were plasticine.
Many rocks on the Earth are distorted into folds. The simplest are
the synclines and anticlines. There
are also other more complex
forms, such as the inclined folds
and turned folds.
Notice this brick wall. A brick is a
piece of clay shaped into a rectangular prism, dried and baked, used
a great deal in the construction of
walls, pillars, ovens, chimneys,
etc., due to its qualities of rigidity,
resistance and endurance. It is
made by extracting clay, grinding,
preparation and kneading, moulding, drying and baking. The clay is
principally composed of aluminium
silicates mixed with iron oxide, calcium carbonate and magnesium.
Notice how the blocks of granodiorite used for this façade are
joined together by another substance. Generally, the blocks used
for façades are joined together
with mortar, but throughout the
history of building this has not
always been so.
Machu-Picchu, the lost city of the
Incas built in the Peruvian Andes,
is one of the finest examples of
Inca architecture. What is most
impressive is the high degree of
perfection of the buildings, especially the religious ones, and above
all the engineering expertise
applied, as many of the rock walls
have a slight inward inclination to
protect them from earthquakes.
Notice this glass façade. Glass can
be formed naturally, by such rapid
cooling of magma that the minerals cannot crystallise, or it can be
synthetic, as we see here.
We say that glass is an amorphous
material because its atoms are not
arranged in a regular pattern. In
contrast, we say that minerals
(such as quartz or diamond) have
a crystalline structure because
their atoms are arranged in an
ordered way. This internal arrangement can be translated into a geometric external form.
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Larvikite
Slate
Migmatite with garnets
Granite
Notice the iridescent brilliance of
the essential mineral (potassium
feldspar) which forms the rock.
Iridescence is an optic phenomenon which forms a play of colours.
It happens when light enters into a
medium in which multiples reflections are produced by the presence of many semitransparent surfaces.
Iridescence is very frequent in
nature. Many minerals show it, but
also some butterflies, some shells,
and it can even be observed in
clouds.
Notice how inside this almost
black slate there are tiny golden
points. If you look at them closely
you see that they are little cubes
with a metallic look. These are a
mineral called pyrite, which crystallises in the cubic system.
Pyrite is an iron sulphide which is
used to obtain sulphuric acid and
iron.
Notice this green migmatite, it can
come from the partial fusion of a
metamorphic rock. You can see
some red grains in it, these are a
mineral called garnet. This name
was given to the mineral in ancient
times because it is the same
colour as pomegranate seeds.
Minerals have many applications in
our daily life. One of the best
known is jewellery, which takes
advantage of different properties
such as hardness, transparency
and the colours which are attractive to our eyes. Garnet is an
example. There are six varieties,
called in gemmology pyrope (red),
almandine (red), spessartine (yellow), grossular garnet (yelloworange), andradite (yellow-green)
and uvarovite (dark green).
Notice the granite of this façade.
For the great civilisations of antiquity, in Egypt and Mesopotamia,
rocks such as granite, dolerite and
diorite were materials much
appreciated in construction.
In ancient Egypt, granite was
quarried in the quarries close to
Aswan (in the south of Egypt) and
was easily transported down the
Nile. Taking advantage of the seasons of flood, boats could carry
huge blocks to the places where
they were to be used, so that they
only had to be taken overland for
relatively short distances. These
expeditions could cover nearly a
thousand kilometres and took one
or two weeks.
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Granite
Quartzite
Veined limestone
Travertine
Notice the grains in this rock,
some are larger than others. This
granite has a porphyritic texture.
We speak of the texture of a rock
when we refer to the relative sizes
of the crystals forming it. For
example, in magmatic rocks we
speak of a granular texture when
the grains are more or less all the
same size and of porphyritic texture when some grains are larger
than others.
Notice the cylinders of an exceptional blue colour inside the shop.
They seem stained, but in fact it is
nature that gives them this colour.
This is a quartzite (metamorphic
rock formed essentially of quartz
grains cemented together by silica)
which owes its blue colour to the
mineral dumortierite. Commercially
the rock is called Blue Macaubas
and is quarried in Brazil. At present
Blue Macaubas is one of the most
prized ornamental rocks.
Notice this rock. For its use in
cladding the façade, the initial rock
has been cut into fine slices.
Ornamental rocks are quarried first
in the form of large blocks and are
then cut into finer pieces to obtain
slabs.
The first great quarry in history was
opened in 2,600 BC, when the
Egyptian King Djoser wanted to
establish his eternal residence in
Sakkara.
The opening of this quarry involved
one of the first geological expeditions to search for all kinds of
rocks popular at that time (highly
coloured and with quite veins, like
the stone we see on this façade).
Notice the cavities formed in this
rock. Inside them you can see
elongated tubes and little holes.
They are moulds of the branches
of plants.
Travertine is a rock resulting from
the precipitation of calcium carbonate, often around stems,
branches and leaves, in river areas
or lakes, or around waterfalls.
In Andorra, this rock is called
“tosca” (and the quarry is a “tosquer”) and historically it was used
a great deal in construction. It can
be seen in the keystones of
Romanesque windows.
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Limestone
Rock?
Calcarenite
White marble
Notice the little fractures filled in
with crystallised minerals showing
in this limestone.
From the moment of its formation,
rock suffers a whole series of
movements and transformations.
No rock has remained undisturbed
throughout its life. The fractures
that you see in this rock were not
always there, they came after its
formation. First the fracture happened and then it was filled in by
the mineral which essentially forms
the rock, that is, calcite.
Generally, fractured ornamental
rocks are more fragile that the
solid types. The fact that the
spaces left by the fractures are
filled in can reduce this fragility.
Notice this material composed of
grains more or less of the same
size. Some even resemble mirrors.
In fact, it is not rock at all.
This is an artificial material marketed since 1990. It is a mixture of
natural stone (94% of quartz) and
ceramics. New technology in the
manufacture of synthetic materials
has enabled us to reproduce the
appearance, touch and weight of
natural stone, and a similar quality.
The most normal applications are
for kitchens and bathrooms, but it
is also used for floors, walls, shop
counters and bars, etc.
Today we can create materials with
such perfection that even the geologists find them difficult to detect !
Notice, on the one hand, how this
rock is composed of small white
grains: these are fragments of the
shells of living beings. Notice, on
the other hand, the red lines; geologists call this cross lamination.
Cross lamination is formed when
sediments are deposited in water
with weak currents. In this case
the shape of these laminations tells
us of the presence of oscillating
currents, that is to say, waves. The
presence of cross lamination and
the fact that the grains composing
the rock are fragments of shells,
tells us that this rock was formed
in a slightly deep marine environment, such as a beach.
Notice this white marble. This metamorphic rock comes from a limestone. If the parent limestone is very
pure, it re-crystallises as white marble, with a texture similar to that of
the sugar. The calcite grains have no
orientation and do not leave any
spaces, that is, the rock is not
porous, a property much appreciated by sculptors. Marble from
Carrara (a town in Italy), for example,
has a very low porosity of between
0.01 and 0.22%. This marble has
been known since ancient times and
has been quarried since that era.
The greatest sculptors of ancient
Greece used it to make such
famous works as the Venus de Milo,
by an unknown artist, and Michelangelo used it in 1501 for his David, a
piece measuring over 4 metres high.
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Granite
Rapakivi granite
Granite
Pegmatite
Notice this rock, quite normally
found on façades, in kitchens and
on shop counters.
Except their geological names, the
rocks used in the world of decoration also have commercial names.
In this case, geologically we speak
of pink biotite granite, and commercially of Pink Porriño. This is a
granite quarried in the municipal
district of Porriño-Mas in the
Spanish province of Pontevedra. In
fact, the Iberian Peninsula is a
large producer of ornamental rock,
with a great variety and quality of
material.
Notice how the texture of this
granite is totally different from the
other granites that you have seen
during this itinerary.
Rapakivi granite has an ovoid texture composed of rounded formations. The centre of these formations, of pink colour, is formed of
alkaline feldspar surrounded by a
paler line of plagioclase.
Many of these granites come from
Finland.
Notice the grains of this rock, all
more or less of the same size. This
granite has a granular texture.
We speak of the texture of a rock
when we refer to the relative sizes
of the crystals forming it. For
example, in magmatic rocks we
speak of a granular texture when
the grains are more or less all the
same size and of porphyritic texture when some grains are larger
than others.
Notice this blue magmatic rock.
Commercially it is called Blue Aran
and it is quarried in the Vall d’Aran
(Spain). It is a pegmatite, a rock
defined as a graphic granite, that
is to say, with an interpenetration
of the minerals (especially the
quartz and feldspar) giving, in section, polygonal shapes recalling
cuneiform inscriptions.
The minerals composing the pegmatite (quartz, feldspar, muscovite
mica and other accessory minerals such as albite, apatite, beryl,
emerald, topaz, tourmaline and
zircon) are of large dimensions
because the rock, when it was
formed, cooled slowly and the
minerals had time to grow.
28
29
32
33
Gabbro
Ornamental rocks
Pink marble
Faults
Notice this black magmatic rock.
This is a gabbro, a plutonic rock
without any quartz, composed
essentially of plagioclase with a
proportion of anorthite (mineral in
the feldspar group, in the plagioclase series) of over half, associated with pyroxenes and iron oxides.
According to the most characteristic mineral, there are several forms
of gabbro: olivine, hornblende,
orthopyroxene, etc. Gabbros are,
in fact, the intrusive equivalent of
basalt (volcanic rock).
Notice the distribution of shapes
and colours in the rocks you can
se in this passage.
Many times we pass by these
rocks without noticing them. In
fact, rocks are natural elements of
great beauty, especially if properly
treated (cut, polished...). And the
great variety of rocks existing on
the Earth (speaking of geodiversity) enables us to make ornamental
combinations of great aesthetic
value.
Notice this pink marble. Marble is
a metamorphic rock derived from
limestone by a re-crystallisation
process.
The impurities present in the limestone during its re-crystallisation
affect the mineral composition of
the resulting marble. The minerals
resulting from these impurities produce a broad variety of coloured
marbles. The purest marble is
white, marble containing hematite
is reddish, marble with limonite is
yellow, and when it contains serpentine it is green. These colours
can be seen as a uniform tint or
can be in veins.
Notice the small discontinuities of
this rock. In this case, we speak of
micro-fractures. On a larger scale,
these discontinuities are called
faults.
Faults form when the rock, under
pressure from movements of the
Earth, is not deformed but breaks
into two sections. Depending on
the movements of these two
blocks of rock and their geometry,
there are vertical, normal, reverse
and transform faults.
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31
34
35
Limestone with stylolites
Granite
Granite
Concrete
Notice the fine wavy lines and the
darker ones crossing this limestone rock. These are stylolites.
Stylolites are structures in the form
of little columns (1 mm to 30 cm
long) which interpenetrate alternately in opposite directions, mostly in limestone rock. They were
formed when the rock was subjected to strong pressure (of sedimentary or tectonic origin) which
meant that dissolution took place
in the weakest parts of the rock.
Stylolites can be blackish or
brown, according to whether the
residues of dissolution are carbonbased or clay-based.
Notice the number of shops in
Meritxell Avenue which use ornamental rocks in their decoration.
However, this use is not new.
Natural stone has been important
throughout the history of humanity,
in building and in art. Rocks have
also been used as magic and religious symbols since the earliest
times in our history.
Notice how some of the plates of
granite rock used to decorate this
façade are polished and others
have a rough surface.
The most frequent finish for ornamental rock is polished, but there
are others, such as flame finished
or bush hammered. The operation
of polishing gives a smooth and
shining surface, using various
abrasive sanders of progressively
find grain. Flame finished is done
by applying temperature of 2,800
ºC to the surface of the rock,
which gives it a rough and glassy
look. For the oldest finish, bush
hammered, the rock surface is
struck with a special hammer with
pyramidal points to give the surface a fine, medium or large rough
texture.
Notice these columns; they are not
stone, but a very common artificial
material, concrete.
Concrete is a construction material
which is the result of a mixture of
gravel, sand, cement and water,
which is then moulded and finally
hardens. Cement is a fine powder
principally made from clay, sand
and limestone. The clay and the
sand supply silicon (Si), aluminium
(Al) and iron (Fe), while the limestone contributes calcium (Ca).
The Romans already used a mixture called Opus caementitium,
composed of limestone clay with
aggregates of puzzolan (volcanic
rock) or laterite flour (sedimentary
rock rich in aluminium and iron),
the precursor of our concrete and
the origin of the term cement.
GRANITE
ARCHITECTURE
ITINERARY
1. Edifici Xavier Maestre
4. Casa Isern
5. Xalet Arajol
Granite architecture is an architectural current which began in the
1930s and lasted until the 1960s.
This current brought a change in
building techniques. Styles moved
from houses built of stone and
subsequently stuccoed, to houses
in which the stone (granite) took on
a leading role: it was left visible
and became a decorative element.
Granite architecture in Andorra
was influenced by Catalan new
century styles, a current which
succeeded modernism in
Catalonia.
In this itinerary we are using the
term “granite architecture”, which
is how the architectural current
was described. It should be said,
however, that geologically speaking the rock used is granodiorite.
Granodiorite is a plutonic magmatic rock composed of quartz (grey
grains), alkaline feldspar and plagioclase (white grains) and biotite
(black grains).
It is thought that the granodiorite
found in Andorra was formed
around 305 million years ago, at a
temperature of around 550 ºC and
at a pressure of some 2.5 kb.
Granite architecture is characterised by the use of granite ashlars. The granite is not placed
uncut as was done before, but is
given a specific shape and
becomes a decorative element in
the whole of the façade or at the
corners and openings.
Granite ashlars are cut square, as
rectangles, rhomboids or honeycomb (the most typical and representative). This last shape can be
seen nearby, behind the chalet, up
the street, on the building which
houses a transformer.
2. Casa Serola
3. Plaça Guillemó
6. Casa Felipó
7. Casa Nyerro
The expansion of granite architecture would not have been possible
without the many stonemasons of
Spanish origin who came to
Andorra, mostly from Andalusia
and Galicia, to build the FHASA
hydroelectric power station (now
FEDA). Some stayed in Andorra,
and others came later, to share in
the large building boom in the
country.
The Plaça Guillemó, called “de les
Arcades”, was conceived by
Bartomeu Rebés Duran, owner of
the land. A draughtsman by training, he laid out here the first example of good town planning in
Andorra la Vella, in the granite
architecture style. The perimeter of
the building was capped by a 40º
cornice, a perimeter porch was set
on the ground floor and balconies
could be constructed on the
façades.
In 1961, the architect Jordi
Masgrau Boschmonar began to
give form to the whole assembly in
the construction of the first building with a covered way.
The development of granite architecture in Andorra is the result,
among other factors, of the availability of this rock.
A large part of the Andorran territory is formed of granodiorites
(called granites in this itinerary)
belonging to the Andorra-Montlluís
batholite. This rock was formed
during the late Carboniferous
epoch, and it is believed to be 305
million years old.
Several quarries supplied the
stonemasons with granite; the
most important was the one in
Santa Coloma.
Granite architecture expanded on
both sides of the Pyrenees: in La
Seu d’Urgell, Ax-Les-Thermes,
Núria and La Molina. It is in
Andorra, however, where it shows
to best effect.
This type of architecture is a reflection of the changes which took
place in the Principality, both
socially and economically, starting
from the 1930s, in shifting from an
essentially rural society to a more
urban society.
8. Casa Massip-Dolsa
9. Casa Cassany
The social and political situation in
Catalonia after the 1930s brought
several Catalan architects to work
in Andorra, where they left their
stamp on the granite architecture.
Among these architects were
Celestí Gusi, Josep Puig i
Cadafalch (Casa Lacruz in
Escaldes-Engordany), Adolfo
Florensa and Xavier Pla, an
Andorran trained in Catalonia.
The Massip-Dolsa house was
planned by Xavier Pla.
In this architectural style, granite is
used not only as a simple construction material, but also with a
clearly decorative purpose. The
granite is used to add decorative
forms and elements to the façade
to give it personality, always seeking symmetry.
This symmetry is well reflected in
the building of the Casa Cassany.
On the ground floor are four semicircular arches, the centre two are
large and are flanked by the two
smaller. On the first and second
floors, the central openings are in
the form of semicircular arches
and those at the sides are with
plain lintels. On the third floor the
pattern is reversed.
10. Hostal Isard
The start of the 20th century saw
the development of a type of elite
tourism, lovers of nature and thermal
waters. Around this new tourism the
first spas in Andorra were opened
and the first luxury hotels designed
to please the exquisite tastes of
these visitors in the new century.
Outstanding among them are the
Hotel Valira (Escaldes-Engordany),
designed by Celestí Gusi, an associate of Puig i Cadafalch, and the
majestic Hotel Rosaleda in Encamp,
designed by Adolfo Florensa.
Also buildings were erected with
other uses, such as the FHASA
hydroelectric power station (now
FEDA), the Radio Andorra broadcasting station (Encamp) and
schools such as the antique
Meritxell School.
Design: m6 & Jordi Pinós - Photos and texts: CENMA (IEA) - DL: AND.198-2007
For more information:
Oficina de Turisme del Comú d‚Andorra la Vella
Plaça de la Rotonda, s/n - AD500 Andorra la Vella
Tel. (+376) 827.117 - [email protected]
www.roquesalcarrer.ad