6787851911 Encyclopædia Britannica, Volume 28 — WitheriteLeonard James Spencer

WITHERITE, a mineral consisting of barium carbonate (BaCO3), crystallizing in the orthorhombic system. The crystals are invariably twinned together in groups of three, giving rise to pseudo-hexagonal forms somewhat resembling bipyramidal crystals of quartz, the faces are usually rough and striated horizontally. The colour is dull white or sometimes greyish, the hardness is 3½ and the specific gravity 4.3. The mineral is named after W. Withering, who in 1784 recognized it to be chemically distinct from barytes. It occurs in veins of lead ore at Hexham in Northumberland, Alston in Cumberland, Anglezark, near Chorley in Lancashire, and a few other localities. Witherite is readily altered to barium sulphate by the action of water containing calcium sulphate in solution, and crystals are therefore frequently encrusted with barytes. It is the chief source of barium salts, and is mined in considerable amounts in Northumberland. It is used for the preparation of rat poison, in the manufacture of glass and porcelain, and formerly for refining sugar.  (L. J. S.)