These are the rocks, which are found at the surface in Andorra, which you will find in the rock garden in Parc Central.

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.

Igneous or magmatic rock
This is formed 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.

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 “another age”. 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”.

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.

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.

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.

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 clay pelite 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 pyrites. 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 mid-20th century. 

Apse of Sant Esteve, Andorra la Vella.

Arajol Chalet, Andorra la Vella.

These are the rocks, which are found at the surface in Andorra, which you will find in the rock garden in Parc Central. 

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.

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.

Quartzite
Quartzite can be a metamorphic rock of silica composition which comes from sedimentary rocks such as quartzarenite and conglomerates.

Conglomerate
Conglomerate is a detritic sedimentary rock, composed by rounded grains measuring over 2 mm.

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.

Pissarra
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.

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.

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.

Limestone
LesLimestone rocks contain more than 50% of calcium carbonate. They are of very different origins, chemical, biochemical and biological. They normally contain many fossils.