1911 Encyclopædia Britannica/Vanadinite
VANADINITE, a mineral consisting of lead chloro-vanadate, (PbCl)Pb4(VO4)3, crystallizing in the hexagonal system and isomorphous with pyromorphite and mimetite (q.v.). The crystals are usually six-sided prisms terminated by the basal planes, but are sometimes modified by numerous pyramidal planes which exhibit parallel hemihedrism. Rounded crystals and groups also occur. The colour is usually light brown or yellow, but crystals from Arizona are bright red. Owing to isomorphous replacement of the vanadium by phosphorus and arsenic, the specific gravity varies from 6.6 to 7.2; a variety containing much arsenic is called endlichite. The hardness is 3. The mineral is one of secondary formation in veins of lead ore. It was first found in Mexico, and in 1801 was asserted to contain a new element, which was called "erythronium"; this was later proved to be identical with the subsequently discovered element vanadium. Other well-known localities are Wanlockhead in Dumfriesshire, Kappel (Eisen-Kappel), near Klagenfurt in Carinthia, Arizona and New Mexico. (L. J. S.)