350 SILICATES. 195. HELVIN.—Helvin; Phillips, Hauy, Hausmann, Hai- dinger. Tetraedrischer Granat; Mohs. Cubic. 0 m - FIG-. 367. oo' 70° 32' 109 28 Pour alternate faces of o are larger than the other four alternate faces. The larger faces smooth, rather curved and uneven, sometimes striated parallel to their edges ; the smaller faces rough, but even. Practure uneven. Trans lucent on the edges. Lustre vitreous, inclining to resinous. Brown, yellow, green of various shades. Streak white. Brittle. II = 6-0...6-6. G = 3-l.,.3'3. Before the blowpipe in the inner flame melts with intu mescence into a yellow opaque bead. With borax in the outer flame fuses into a transparent violet glass. With salt of phos phorus yields a skeleton of silica. With soda on platinum foil becomes green. Is decomposed by hydrochloric acid with evo lution of sulphuretted hydrogen, and forms a jelly of silica. 3ll J S + MnSu, where li is glucine and protoxides of iron and manganese. Analyses by C. Gmelin :— Silica 33-26 35-27 Glucine 12-03 9-47 Protoxide of iron . . . 5-56 7-99 Protoxide of manganese . 44 68 42 13 Sulphur 5-06 — Is found in attached and imbedded crystals, in a bed in gneiss at Schwarzenberg in Saxony. It is said to occur also on the Kalte Kober near Breitenbrunn in Saxony, and at Hortekulle near Modum in Norway. 196. ETJLYTINE.—Bismuth blende; Phillips. Bismuth silicate; Dufrenoy. Dodekaedrische Demant-Blende ; Mohs. -aaeselwismuth ; Hausmann. Eulytin ; Haidinger. Cubic. 1 JV"?’ f on.cleavage, 0 ill, n 211. The forms 0, n are nemihedral with inclined, faces.