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Granitic chaos of Mont Lozere
In geomorphology (scientific study of the reliefs and processes that shape them, on the telluric planets), a chaos of blocks or balls designates a model of loosening blocks or rocks released by erosion. These forms are part of the products of weathering (alteration of rocks by exposure to atmospheric agents), like the tors, the arenas and on a higher scale the inselbergs.
To understand the alteration of the granite, it is necessary to know its structure. This is a magmatic rock with a granular structure, completely crystallized and whose crystals are clearly visible to the naked eye. The word "granite" comes from elsewhere from the Latin granum, grain.
The granular minerals that make up granite are of several types:
- mainly quartz, it is pure silica.
- micas: they are laminated minerals. We have mostly black mica, but also white mica. White mica is especially rich in aluminum and potassium, whereas black mica is especially rich in magnesium, potassium and iron.
- feldspars: potassic feldspars and plagioclase feldspars.
- a number of other minerals can also be found in granite (hornblende, garnets, magnetite, apatite, zircon).
Granitic chaos evolves with the crystallization and deep cooling of a granitic intrusion, creating a network of mainly orthogonal shrinkage faults at depth: these diaclases (episode in which a rock splits without the disjointed parts moving away from each other, not to be confused with the fault.) then debited the intrusive granite into parallelepipedal blocks. When the erosion of the softer neighboring rocks is flush with the granitic pluton, the surface waters erode this granite massif.
Deep erosion hydrolyzes feldspars into clay, which breaks up granite into a granite arena, erosion on the surface by water that seeps into more or less large crevices eventually bursting the rock. This phase is followed by quaternary gelation.
Gelifraction, or cryoclasticity, is the result of successive phases of freezing and thawing on elements located in the soil or within a rock in place. This leads to the formation of parallelepiped granite blocks that continue to erode. The result is stones of all sizes, balls of stones (formation of tors) which end up piling up to each other in sometimes precarious balances or to dissociate completely and accumulate to form a granite chaos in form of «castle» While the sliding of the blocks on the slopes form the «slope chaos».