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Sedimentary rocks

Sandstone: is detrital (clastic) sedimentary rock made of sand-sized grains (0.062 to 2 mm). Sandstones can be composed of grains with diverse origin: quartz, feldspar, calcite are typical constituents.  They are mostly lithifified by the cementation (calcium carbonate, silica, iron oxide) of sands.

Conglomerate: is detrital (clastic) sedimentary rock made of rounded gravel-sized clasts (> 2 mm). The rock containing angular-shaped gravels, is called breccia. They are mostly cemented and contain a matrix (finer grained sediments), such as sand, silt or clay, which fills the pores between the clasts.

Limestone: is a chemical sedimentary rock made of the mineral calcite (CaCO3). It is formed by the direct precipitation of calcite from water containing dissolved calcium. This can take place through both biological and nonbiological processes.

Dolostone: is a chemical sedimentaty rock that contains the mineral dolomite (CaMg(CO3)2). Most of them are formed as a magnesium replacement of calcium in limestones before lithification, a process called dolomitization.

Igneous rocks

Granite: intrusive igneous rock with a phaneritic texture (coarse-grained: visibles crystals) which consists mainly of quartz, feldspar (and plagioclase) and mica (felsic composition). It is formed underground (some km below surface) by the slowly cooling of magma.

Diorite: intrusive igneous rock with a phaneritic texture (coarse-grained: visibles crystals) which consists mainly of amphibole and plagioclase (intermediate composition). It is formed underground (some km below surface) by the slowly cooling of magma.

Andesite: extrusive (volcanic) igneous rock with an aphanitic texture (fine-grained: small crystals non visible to the naked eye), although a porphyritic texture (large crystals known as phenocrysts surrounded by a fine-grained matrix or groundmass of microscopic crystals, indicating two phases of crystallization) is also common.  It is constitued mainly of amphibole and plagioclase minerals (intermediate composition). It is formed during volcanic eruptions or near the surface by the rapid cooling of magma.

Basalt: extrusive (volcanic) igneous rock with an aphanitic texture (fine-grained: small crystals non visible to the naked eye) which consists mainly of pyroxene, plagioclase and olivine (mafic composition). It is formed during volcanic eruptions or near the surface by the rapid cooling of magma.

Gabbro: intrusive igneous rock with a phaneritic texture (coarse-grained: visibles crystals) which consists mainly of pyroxene plagioclase and olivine (mafic composition). It is formed underground (some km below surface) by the slowly cooling of magma.

Metamorphic rocks

Gneiss: is a foliated metamorphic rock which shows a banded texture characterized by alternating darker and lighter colored bands made of felsic (such as feldspar or quartz) and mafic minerals (ferromagnesian), respectively. This metamorphic rock is formed under high-temperature and high-pressure.

Quartzite is a non-foliated metamorphic rock which was originally a sandstone made mainly of quartz. This metamorphic rock is formed through increasing pressure and heating  usually related to compresive stresses.

Marble: is a non-foliated metamorphic rock which was originally a limestone (or dolostone). This metamorphic rock is formed through increasing pressure and temperatura (regional) and heating (thermal).