Oliverio Conant
The chalk is a Sedimentary rock containing almost exclusively Calcaire CaCO3 and a little Argile.
When limestone and clay are in about equal proportions, one speaks rather about marl.
The chalk was formed by accumulation of skeletons of marine micro-organisms, Coccolithe S primarily, with the geological time of the Crétacé to which it gave its name. For this reason, the chalk belongs to the geological Puits of carbon and she plays a big role for the cycle of calcium. During the Cretaceous higher (between -100 and -65 million years), of important layers of chalk settled on current the Paris basin.
The chalk is permeable, porous and friable.
The layers of chalk are often Aquifère S. It is thus of the Ground water of the Artois or that, gigantic, of the Beauce which covers 9 000 km ².
Materials resembling chalk
The chalk was used in the form of sticks to write on the black boards classrooms in the school S. Aujourd'hui, the chalks used for teaching are an agglomeration of chalk crushed (Carbonate of calcium) or of Plâtre, added with pigments for chalks of color.
The chalk of the tailors is containing Talc.
The chalk is also used like Matériel of painting. More or less fatty or dries, it is presented in sticks or in the form of Parallélépipède S. It is generally applied directly to paper. The chalks gray are often used for drafts, while the chalks coloured allow a work rather close to the Pastel S the oil.
The chalk also gets busy with the Billard to prevent the slip of the end of the tail on the struck ball, thus making it possible to give him effects.
External bonds
- Formation and exploitation of the chalk
Simple: Chalk
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