ANHYDRITE, a mineral, differing chemically from the more commonly occurring gypsum in containing no water of crystalli zation, being anhydrous calcium sulphate, It crystallizes in the orthorhombic system, and has three directions of perfect cleavage parallel to the three planes of symmetry. Distinctly developed crystals are somewhat rare, the mineral usually present ing the form of cuboidal cleavage masses. The hardness is 31 and the specific gravity 2.9. The colour is white, sometimes greyish, bluish, or reddish. On the best developed of the three cleavages the lustre is pearly, on other surfaces it is of the ordinary vitreous type.
Anhydrite is most frequently found in salt deposits, but it is only met with at some depth; nearer the surface it has been altered to gypsum owing to absorption of water.
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.