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QTTAETZ. 245 85° 30'). The existence of these forms is, however, for the reason above mentioned, extremely doubtful. 12G. PERICLASE.—Periclase; Dufrenoy. Periclas; Haus- mann, Haidinger. Cubic. a 100 cleavage, 0 ill. 90° 0' aa 00 oa 70 32 64 44 Cleavage, a, very perfect. Trans parent. Lustre vitreous. Dark green. 11 = O'O. <j = 376. Infusible before the blowpipe. In powder soluble in acids. Mg, magnesium 01'20, oxygen 38-80. tig. 268. Analyses a by Scacchi, b, cby Damour:— a b C Magnesia . . . 89-04 92-57 91-18 Protoxide of iron . 8-58 6-22 5-67 Insoluble matter . — 0-86 2-10 Was found on Monte Somma near Naples. 127. QUARTZ.—Quartz ; Phillips. Rhomboedrischer Quarz ; Mohs. Quarz ; Ilauy, Hausmann, Haidinger. Hhombohedral. 100,111 = 61° 47'. (yd} . 0 ill twin-face, a 011, k 11 4 7, r 100, z 122, s 142, 1 °n, d 411, ji 13 2 2, l_ ill, \ 5ll, m 722, y 311, J 833, ^ 13 5 5, h 433, <j> 13 8 8, p 744, V _16 6 8, X 412, y '»U, u 814, t 4 11 2, 0 14 22 7, p 10 14 6, e 452, W H 10 7, q 16 17 8, u 221, n 854, £ 261, 3 22 19 2, ? Uua. The forms v, x, y, u, s, t, p, 0, w, q, p, n are hemihedral with •^symmetric faces, occurring in one only of the two zones r'z'b, z b, and in the same alternate luneB between b, b", b\... . m 3