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 .