CROCOITE  , a

mineral consisting of lead chromate, PbCrO4, and crystallizing in the monoclinic system . It is sometimes used as a paint, being identical in composition with the artificial product chrome-yellow; it is the only chromate of any importance found in nature . It was discovered at Berezovsk near Ekaterinburg in the Urals in 1766; and named crocoise by F . S . Beudant in 1832, from the Greek Kp6KOr, saffron, in allusion to its colour, a name first altered to crocoisite and afterwards to crocoite . It is found as well-developed crystals of a bright hyacinth-red colour, which are translucent and have an adamantine to vitreous lustre . On exposure to light much of the translucency and brilliancy is lost . The streak is orange-yellow; hardness 4-3; specific gravity 6•o . In the Urals the crystals are found in quartz-veins traversing granite or gneiss: other localities which have yielded good crystallized specimens are Congonhas do Campo near Ouro Preto in Brazil, Luzon in the Philippines, and Umtali in Mashonaland . Gold is often found associated with this mineral . Crystals far surpassing in beauty any previously known have been found in the Adelaide Mine at Dundas, Tasmania; they are long slender prisms, 3 or 4 in. in length, with a brilliant lustre and colour . Associated with crocoite at Berezovsk are the closely allied minerals phoenicochroite and vauquelinite .

The former is a basic lead chromate, Pb3Cr2O9, and the latter a lead and

copper phosphate-chromate, 2(Pb,Cu)CrO4 . (Pb,Cu)3(PO4)2 . Vauquelinite forms brown or green monoclinic crystals, and was named after L . N . Vauquelin, who in 1797 discovered (simultaneously with and independently of M . H . Klaproth) the element chromium in crocoite . (L . J .