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ATJGITE. 291 FIG. 314. Combinations. cm, cab, cabm, sma.p.o.z.b, nmab..cp,om..c.sp.z.\.a, cpuoab..s.mf,somab. The faces c,p usually rough; % curved; a, b striated parallel to their inter- sectionswith eachother; °> striated parallel to their intersections with *• Twins. Twin-face a. Cleavage, m, tolerably perfect, but interrupted; a i b less distinct ; s, occasionally. Planes of union, but not of true cleavage, occur frequently in some varie ties parallel to c. Fracture conchoi dal... uneven. Transparent... opaque. Lustre vitreous. For rays in a plane parallel to b, and polarized in that plane, q = reso. The optic axes lie in a plane parallel to b. One makes angles of 80° 34' and 6° 36' with normals to a and c respectively; the other makes angles of 21° 38' and 52 21' with normals to a and c respectively. Colourless, white, usually coloured, grey, green, black. Streak white...grey. Brittle, n = 5-0...co. g = 32. ..3-4. Before the blowpipe melts into a white, grey, green or black glass. With borax and salt of phosphorus usually yields the reaction of iron. With solution of cobalt the white and colour less varieties become red. Is but slightly acted upon by acids. CaSi + RSi, where It consists essentially of Mg and Fe. Analyses of the grey and green transparent varieties called uiopsido a from the Fassathal by Waekenroder, b from Orijerfvi 7^1. Rose, e from Langbanshytta in Wiirmland by H. Rose, “ from Tammare in Finland by v. Bonsdorff, e from Achma- °Wsk, g = 3‘28, by Hermann, f from the Brazils by Kussin :— Silica ■Lime . Magnesia f rotox. iron . * rotox. mang. Alumina . a b c d e / 64-15 64-64 65-32 54-83 63-97 66-61 24'74 24-94 23-01 24-76 26-60 25-11 18-22 18-00 18-99 18-55 17-86 17-82 2-60 1-08 (#* 2-16) 0-99 2-00 1-20 0-18 2-00 1-69 0-32 0-57 — 0-20 o 2 — 0-28 — —