A rock is a material formed by a natural aggregate of mineral, Fossiles, and/or elements of other (S) rock (S).
The Pétrographie (of the Greek will petra , stone, and graph , description) is the Science of description and of the analysis of the rocks, whereas the Pétrologie (of the Greek will petra and logo , study) is the science which studies the mechanisms of formation and transformation of the rocks. Science associated with and the deformation motion study with the rocks is called the Rock mechanics .
ClassificationThe rocks are classified according to their composition, their origin or the method of their formation; initially in three main categories:
- the magmatic rocks (also qualified the igneous ones or the eruptive ones) formed by the solidification of magma S, of which:
- the volcanic rocks or extrusives or effusive , brutally cooled surfaces some after an volcanic eruption, hemicrystalline;
- the plutonic rocks or intrusive which cooled in-depth, slowly and without degasification in the magmatic room, and are thus holocrystalline;
- the slickenside rocks or hypoabyssales ( hypabyssales ), intermediaries between the extrusives and intrusive rocks, and having undergone a partial degasification.
- the sedimentary rocks, formed on the surface of the Earth or in the seas by accumulation in layers of materials under the action of agents exogenic, like the wind and water;
- the metamorphic rocks or cristallophylliennes formed by the recrystallization (and generally the Déformation) of sedimentary rocks or magmatic under the action of the temperature and of the pressure which grow with the depth in the Earth's crust or in contact with other rocks.
One can also classify the rocks in three types, according to their properties:
- movable rocks like the Sand or the Clay
- friable rocks like the Chalk
- coherent rocks such as the Granite
The rocks are more or less hard: thus, the Talc and the Gypse are very sensitive to erosion, whereas the Corindon and the Diamant are very resistant.
The homogeneity of the rocks varies according to minerals: one distinguishes four types of textures:
- grained texture (granite)
- texture prophyroïde
- texture microgrenue (Batholite)
- vitreous texture (basalt)
The rocks can more or less dilate.
UseThe rocks have many uses, in particular:
- the Rockwool, excel heat insulator and accoustic containing volcanic rock;
- stones to be built (stones of size and hardcores);
- the Aggregate S;
- the Sculpture S and ornaments;
- the extraction of Ore S;
- the Rock salt.
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