Once contemptuously styled common garnet, andradite suddenly sprang into the rank of precious stones upon the discovery some thirty years ago of the brilliant, green stones (Plate XXIX, Fig. 7) in the serpentinous rock beside the Bobrovka stream, a tributary of the Tschussowaja River, in the Sissersk district on the western side of the Ural Mountains. The shade of green varies from olive through pistachio to a pale emerald, and is probably due to chromic oxide. Its brilliant lustre, almost challenging that of diamond, and its enormous colour-dispersion, in which respect it actually transcends diamond, raise it to a unique position among coloured stones. Unfortunately its comparative softness limits it to such articles of jewellery as pendants and necklaces, where it is not likely to be rubbed. When first found it was supposed to be true emerald, which does actually occur near Ekaterinburg, and was termed ‘Uralian emerald.’ When analysis revealed its true nature, it received from science the slightly inharmonious name of demantoid in compliment to its adamantine lustre. Jewellers, however, prefer to designate it ‘olivine,’ not very happily, because the stones usually cut are not olive-green and the name is already in extensive use in science for a totally distinct species (p. 225); they recognized the hopelessness of endeavouring to find a market for them as garnets. The yellow kind of andradite known as topazolite would be an excellent gem-stone if only it were found large and transparent enough. Ordinary andradite is brown or black, and opaque; it has occasionally been used for mourning jewellery. The specific gravity varies from 3·8 to 3·9, being about 3·85 for demantoid, which has a high refractive index, varying from 1·880 to 1·890, and may with advantage be cut in the brilliant form. It is the softest of the garnets, being only 6½ on Mohs’s scale. (_g_) UVAROVITE This variety, which is altogether unknown in jewellery, is a calcium-iron garnet corresponding mainly to the formula Ca_{3}Cr_{2}(SiO_{4})_{3}, but with some alumina always present, and was named after a Russian minister. It has an attractive green colour, and is, moreover, hard, being about on Mohs’s scale, but it has never yet come to light of a size suitable for cutting. The specific gravity is low, varying from 3·41 to 3·52. Unlike the kindred varieties it cannot be fused by heating before an ordinary blowpipe. CHAPTER XXIV TOURMALINE (_Rubellite_)