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CROCOITE

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Originally appearing in Volume V07, Page 479 of the 1911 Encyclopedia Britannica.
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CROCOITE , a See also:

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

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

End of Article: CROCOITE

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