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“liis! SI COBUHDUSt. 243 io 69° l' po 68 2 rr ) 93 66 W 47 26 ss' 111 16 vv f 69 44 60' 69 24 zz 68 55 vv 57 38 KK 66 68 wuf 66 0 cc 63 46 nix’ 51 68 PV 9 14 rd 43 2 nr 49 66 vd 74 37 ra 90 0 ia 73° 42' nd 64° l' ga 69 66 as" 29 22 FIG. 267. Combinations, oa, or, ar, rn, zn, ora, orn, ore, onz, orna, ornz, nsva, ornab, ohzQa, oarr\np, oarn^vgs. The faces o are striated parallel to their intersections with r, and sometimes parallel to their intersections with a. The faces of the zones oo deeply striated parallel to their intersections with each other. Twin crystals. Twin-face r; frequently repeated in parallel layers. Cleavage, r, o, in many varieties perfect, but interrupted. The planes r are frequently merely faces of union. Fracture conchoidal...uneven. Transparent...translucent on the edges. Lustre vitreous ; o in some varieties pearly, fi = 1-769, f* = 1-762. Colourless, white, usually blue or red, also green, yellow, brown, grey. Sometimes different parts of the same crystal have different colours, as blue and red, blue and white, red and w-hite. Some varieties are opalescent, and show a six- rayed star, having its centre in the axis of the crystal, especially when the end is ground convex. By transmitted light some varieties appear green in the direction of the axis, and blue in a direction perpendicular to the axis. On looking through a blue crystal in a direction parallel to o, its colour is prussian blue when the light is polarized in a plane perpendicular to o, and light green when the light is polarized in a plane parallel to o. ■A- red crystal viewed in the same manner is red or very light hrown, according as the light is polarized in a plane perpen dicular or parallel to o. ii =9'0. g = 3-93...4‘08. Infusible before the blowpipe either alone or with soda. Soluble in borax and salt of phosphorus with great difficulty, hut perfectly, forming a transparent glass. With solution of M 2 ji