CLASSIFICATION OF ROCKS:The three sets of rocks

The three sets of rocks:

The Sedimentary rocks:

- Are layered

- Are not fully crystallized

- Sometimes contain fossils

Magmatic rocks:

- Are layered

- Do not contain fossils

- Plutonic igneous rocks are fully crystallized

- Volcanic magmatic rocks are partially crystallized

Metamorphic rocks:

- Are layered (sheets oriented in the orientation of minerals)

- Are fully crystallized

- Do not contain fossils

Sedimentary Rocks:

Sedimentary rocks have four possible causes:

- Detrital origin: they are siliceous and result from the accumulation of particles from continental erosion (eg sandstones and sands)

- Biochemical origin: they are siliceous and carbonate or result from the accumulation of fossils (tests and skeletons of protozoa, molluscs ...) (example: marl)

- Origin authigène: it is due exclusively to chemical processes such as evaporation (eg gypsum, potash ...)

- Biological Origin: they are carbonated and result from the accumulation and processing of organic plant matter. (Eg coal, petroleum ...)

Some criteria for determination of sedimentary rocks:

- Furniture and permeable rocks: The Sands

- Loose rock: marl

- Soluble rocks: gypsum ...

- Rocks reacting to the cold acid: carbonate rocks

- Fuels rocks: hydrocarbons

Magmatic Rocks:

The origin of magmas: the liquid provided by the partial melting is less dense than the surrounding materials. This partial merger may take place in the continental crust, we obtain a granite or liquid in the upper mantle, we get a basaltic andesite or liquid.

Magma thus formed therefore migrates to the surface it reaches or not. If the magma

does not reach the surface, it crystallizes giving igneous plutonic rocks.

If the magma reaches the surface, it will crystallize giving magmatic rocks

volcanic.

One class magmatic rocks in the triangle of Streckeisen:

Metamorphic Rocks:

Metamorphic rocks are from the structural transformation and / or inorganic, solid state, of pre-existing rocks subject to new conditions of pressure and temperature. Among these rocks can be distinguished:

- Those who have had a weak metamorphism: they are generally greenish in color and contain chlorite and sericite. (Eg shale (paradérivés) métagranites (orthodérivés))

- Those who have had a strong metamorphism: they contain characteristic minerals such as biotite, garnet, kyanite or glaucophane ... (Examples: mica schist and gneiss (paradérivés), amphibolites and gneiss (orthodérivés))

The metamorphic history is not the same as sedimentary or magmatic origin of the initial rock. The amplitude of metamorphism depends on the presence or absence of water.

Metamorphic facies: