The rocks are the association of one or more minerals . They are produced by geological processes. Rocks are constantly modified by the action of different geological agents, such as water or wind, and by living beings.
The rocks are classified according to their properties:
The igneous rocks are the result of the solidification of magma. Magma is a molten mineral mass, that is to say it has a certain fluidity. Magma contains both minerals and volatiles and dissolved gases.
Igneous rocks can be intrusive or extrusive:
- The intrusive rocks , also called plutonic, are the most abundant and form the deeper parts of the crust.
- The extrusive rocks , volcanic also called, are formed as a result of cooling lava on the surface of the earth.
Examples of igneous rocks
- Granite (plutonic): gray or light red. Composed of quartz, potassium feldspar and mica.
- Porphyry (plutonic): dark red. Composed of feldspar and quartz.
- Gabbro (plutonic): thick texture. It consists of calcium plagioclase, pyroxene, olivine, hornblende and Hypersthene.
- Sienite (plutonic): it is distinguished from granite because it does not contain quartz. Contains feldspar, Oligoclase, albite and other minerals.
- Diorite (plutonic): intermediate composition: two thirds of plagioclase and one third of dark minerals.
- Peridotite (plutonic): dark colored and high density. Composed almost entirely of pyroxene.
- Tonalite (plutonic): composed of quartz, plagioclase, hornblende and biotite.
- Basalt (volcanic): dark colored, composed of magnesium and iron silicates, in addition to a low silica content.
- Andesite (volcanic): dark gray or intermediate. Composed by plagioclase and ferromagnetic minerals.
- Rhyolite (volcanic) of brown, gray or reddish colors. Formed by quartz and potassium feldspar.
- Dacite (volcanic): high iron content, is composed of plagioclase feldspar.
- Traquita (volcanic): composed of potassium feldspar and plagioclase, biotite, pyroxene and hornblende.
Sedimentary rocks are formed from the alteration and destruction of other rocks that previously existed. In this way, residual deposits are formed that can remain in the same place where they originate or that are transported by water, wind, ice or ocean currents.
Sedimentary rocks are formed by diagenesis (compaction cementation) of sediments . The different sediments form strata, that is layers formed by deposit.
Examples of sedimentary rocks
- Gap: Detritic sedimentary rock, composed of angular fragments of rock larger than 2 millimeters. These fragments are joined by a natural cement.
- Sandstone: Detritic sedimentary rock, of different colors, which contains clasts of sand size.
- Shale: Detritic sedimentary rock. Composed of clastic debris, in particles the size of clay and silt.
- Marga: composed of calcite and clays. It usually has a whitish color.
- Limestone: composed mainly of calcium carbonate. It can be white, black or brown.
Metamorphic rocks are those produced by the evolution of a rock above was subjected to an atmosphere energy very different from the formation (for example, more hot or cold, or by a significant change of pressure).
Metamorphism can be progressive or regressive. Progressive metamorphism occurs when the rock is subjected to a higher temperature or higher pressure, but without melting.
Regressive metamorphism occurs when a rock that evolved at great depth (where there is greater pressure and heat) and when approaching the surface becomes unstable and evolves.
Examples of metamorphic rocks
- Marble : compact metamorphic rock that evolved from limestone rocks subjected to high temperature and pressure. Its basic component is calcium carbonate.
- Gneiss : composed of quartz, feldspar and mica. Its composition is equal to that of granite but forms alternating layers of clear and dark minerals.
- Quartzite : hard metamorphic broken with high quartz content.
- Amphibolite : the oldest rocks found.
- Granulite : formed by a process of high temperatures. Of whitish color, with maroon inlays. They are found in the oceanic ridges.