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Anhydrite is a mineral - anhydrous calcium sulfate, CaSO₄. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetrySymmetry is a characteristic of geometrical shapes, equations and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. The three main symmetri. Distinctly developed crystalThis article is about the form of solid matter. For other uses of this word, see Crystal (disambiguation . Insulin Crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extends are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The colour is white, sometimes greyish, bluish or purple. On the best developed of the three cleavages the lustre is pearly, on other surfaces it is vitreous. When exposed to water, anhydrite readily transform to the more commonly occurring gypsumGypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO 2HO. Chemical structure Heating gypsum above approximately 150°C (302°F) partially dehydrates the mineral, by driving off exactly 75% of the water containe, (CaSO₄-2H₂O) by the absorption of water. Anhydrite is commonly associated with calciteThe mineral calcite is a carbonate of calcium corresponding to the formula CaCO and is one of the most widely distributed minerals on the Earth's surface. It is a common constituent of sedimentary rocks, limestone in particular. It also occurs as a vein m, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposites.

Anhydrite is most frequently found in salt deposits with gypsum; it was, for instance, first discovered, in 1794, in a salt mine near Hall in Tirol. In this occurrance depth is critical since nearer the surface anhydrite has been altered to gypsum by absorption of circulating ground water.

From an aqueous solution calcium sulfate is deposited as crystals of gypsum, but when the solution contains an excess of sodium or potassium chloride anhydrite is deposited. This is one of the several methods by which the mineral has been prepared artificially , and is identical with its mode of origin in nature, the mineral is common in salt basins.

The name anhydrite was given by A. G. Werner in 1804, because of the absence of water of crystallization, as contrasted with the presence of water in gypsum. Other names for the species are muriacite and karstenite; the former, an earlier name, being given under the impression that the substance was a chloride (muriate). A peculiar variety occurring as contorted concretionary masses is known as tripe-stone, and a scaly granular variety, from Vulpino , near Bergamo, in Lombardy, as vulpinite; the latter is cut and polished for ornamental purposes.