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Hornblende or amphibole, like augite, is of formula R"Si0 3 . Its varieties are tremolite, grammatite, actinolite, smaragdite, pargasite, arfoedsonite, asbestos, amianthus, uralite, nephrite. Leucite is K 2 O. A1 2 3 . 4Si0 2 . Turning to the formula R // 2 SiO 4 we have the olivine, peridote, tephroite, willemite, dioptase (with 1H 2 O). Garnet is3R" 2 Si0 4 R'" 2 Si 3 2 , and idocrasemuch the same but with water. Nepheline has the formula 2NaKO. 2A1 2 3 . 5Si0 2 ; sodalite, 3Na 2 Si 2 8 + 2NaCl ; hatiyne and nosean are like nepheline, but containing sodium or calcium sul- phates. The scapolites are all silicates of lime and potash or soda. CERAMIC CHEMISTRY. 9 The micas include biotite, lepidomelane, phlogopite, zinnwaldite, lepidolite, muscovite, paragonite, margarite. We have already dealt with most of them. Chlorite is 4R // 0. A1 2 3 . 2Si0 2 . 3H 2 O, where R" is Mg or Fe. The basic silicates, those containing less than 40 per cent, of silica, comprise chondrodite, humite, andalusite, cyanite, staurolite, tourmaline, axinite, datholite (the last three containing borate), topaz (which has from 16 to 20 per cent, of fluorine), and the epidote group. As Orton and Mellor have pointed out, the nomen- clature of silicates is in urgent need of standardisation.