Anhydrite
The anhydrite is a Minéral composed of natural sulfate of Calcium (CaSO4), crystallizing in the crystalline Système orthorhombic, Groupe of space Amma .
Mineral of the évaporite S, anhydrite seldom gives well formed crystals. It is formed instead of the Gypse if the solutions are very concentrated, or like secondary Minéral, by dehydration of the Gypse. Anhydrite can recognize Gypse because it raye not with the nail, inter alia.
The uses of anhydrite are limited: modifier of the ground, delaying Cement Portland cement, presses pie of Soja (Tofu) basic quality, instead of the Nigari. Previously anhydrite was used as source of Soufre for the sulphuric production of Acid.
Natural anhydrite, or artificial the by-product of various industrial processes, can be used to carry out covers in the buildings, said " covers anhydres" or " covers of anhydrite". They are more and more used of share their rather weak cost, their good compatibility with the systems of heating floors modern their great speed of catch, and their fluidity which allows a high degree of accuracy. On the other hand they keep the absorbent properties of starting material.
Note on the structure
In the Carbonate S, the calcic member takes two structures, Calcite (typical of the cations smaller than the Calcium) and Aragonite (typical of the cations larger than the Calcium). On the other hand, in the Sulfate S the calcic member takes only the structure anhydrite, whereas the members with larger cations take the structure Barite. NaClO4 takes the structure anhydrite, whereas Chlorate S, Manganate S, Sélénate S and Chromate S of Potassium, Baryum and Strontium take the structure Barite.
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