The Collaborative International Dictionary
Anhydrite \An*hy"drite\, n. [See Anhydrous.] (Min.) A mineral of a white or a slightly bluish color, usually massive. It is anhydrous sulphate of lime, and differs from gypsum in not containing water (whence the name).
Wiktionary
n. (context mineral English) A saline evaporite consisting of anhydrous calcium sulfate (gypsum).
Wikipedia
Anhydrite is a mineral—anhydrous calcium sulfate, CaSO. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium ( baryte) and strontium ( celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The color 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 transforms to the more commonly occurring gypsum, (CaSO·2HO) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to ~200°C under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.
Usage examples of "anhydrite".
Evaporite deposits of anhydrite and gypsum were formed in the circum-Atlantic rifting and circum-Tethyan zones, and evoke a picture of coastal deserts such as near the modern Red Sea.
All around them were the many-colored rocks of the continental roots and glistening, fantastically eroded shapes of salt and anhydrite and gypsum.