COBALTITE  , a

mineral with the composition CoAsS, cobalt sulpharsenide . It is found as granular to compact masses, and frequently as beautifully developed crystals, which have the same symmetry as the isomorphous mineral pyrites, being cubic with parallel hemihedrism . The usual forms are the cube, octahedron and pentagonal dodecahedron {210} . The colour is silver-white with a reddish tinge, and the lustre brilliant and metallic, hence the old name cobalt-glance; the streak is greyish-black . The mineral is brittle, and possesses distinct cleavages parallel to the faces of the cube; hardness 51; specific gravity 6.2 . The brilliant crystals from Tunaberg in Sodermanland and Hakansboda in Vestmanland, Sweden, and from Skutterud near Drammen in Norway are well known in mineral collections . The cobalt ores at these localities occur with pyrites and chalcopyrite as bands in gneiss . Crystals have also been found at Khetri in Rajputana, and under the name sehta the mineral is used by Indian jewellers for producing a blue enamel on gold and silver ornaments . Massive cobaltite has been found in small amount in the Botallack mine, Cornwall . A variety containing much iron replacing cobalt, and known as ferrocobaltite (Ger . Stahlkobalt), occurs at Siegen in Westphalia . (L .

J .