CROCIDOLITE, a mineral described in 1815 by M. H. Klaproth under the name Blaueisenstein (blue ironstone), and in 1831 by J. F. Hausmann, who gave it its present name on account of its nap-like appearance (Gr. KpOKUS, nap of cloth). It is a blue fibrous mineral belonging to the amphibole group and closely related to riebeckite ; chemically it is an iron sodium silicate. Its resemblance to asbestos has gained for it the name Cape Asbestos, the chief occurrence being in South Africa. The mineral suffers alteration by removal of alkali and oxidation of the ferrous iron, and further by deposition of silica between the fibres, or by their replacement by silica ; a hard siliceous mineral is thus formed which when polished shows, in consequence of its fibrous structure, a beautiful chatoyance or silky lustre. This is the ornamental stone which is known when blue as "hawk's eye," and when of rich golden brown colour as "tiger-eye." The latter, which represents the final alteration of the crocidolite, has become 'ery fashionable as "South African cat's eye," and is often termed "crocidolite," though practically only a mixture of quartz with brown oxide of iron.