Calcium Selenate, CaSeO₄

Calcium Selenate, CaSeO₄, can be obtained as transparent or milk-white rhombic prisms, showing double refraction, by fusion of an alkali. selenate with sodium and calcium chlorides. It can only be fused with difficulty in the blow-pipe, and it is slowly attacked by hydrochloric acid with evolution of chlorine. The density is 2.93 and the hardness 3.5.

The dihydrate, CaSeO₄.2H₂O, in monoclinic crystals isomorphous with gypsum, is obtained by mixing solutions of potassium selenate and calcium nitrate and boiling, when the crystals, being less soluble in hot water than in cold, are deposited. When dehydrated by heat and treated with water, it sets like plaster. The density is 2.676.