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 Cape Colony . The mineral suffers alteration by removal of alkali and peroxidation 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 con-sequence 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 very fashionable as " South African cat's eye," and is often termed " crocidolite," though practically only a mixture of quartz with brown oxide of iron . The following are analyses by A . Renard and C .

Klement of the unaltered crocidolite and of the blue and brown products of alteration: Crocidolite . Hawk's-eye . Tiger-eye . Silica ~— 51'89 93 45 93 05 Ferric oxide 19.22 2.41 4.94 Alumina . . . . .. 0.23 0.66 Ferrous oxide . 17.53 1.43

Magnesia . 2.43 0.22 0.26 Lime 0.40 0.13 0.44 Soda 7.71 Potash 0.15 Water 2.36 0.82 0.76 Total . . Io1.69 98.69 Ioo•11 Another alteration product of the crocidolite, consisting of silica and ferric hydrate, has been called griqualandite . Crocidolite and the minerals resulting from its alteration occur in seams, associated with magnetite and other iron-ores, in the jasper-slates of the Asbestos Mountains in Griqualand West, Cape Colony . It is known also from a few other localities, but only in subordinate quantity .