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566 CAEBONATES. Combinations. pi..m.a.r, mi.a.y, mpia..c.v.z, pmia.z.x.r.by, bwmpsryoTcixac. The faces p sometimes striated parallel to their intersections with i or is; the faces a almost always striated parallel to their intersections with i, and also slightly parallel to their intersections 'with m; x, fc, i, v, z striated parallel to their intersections with each other; c, usually rough. Twins. Twin-face m. Cleavage, m, i, tolerably perfect; a, a:, traces. Fracture conchoidal. Transparent...translucent. Lustre adamantine...resinous, b = 1 , 813...2'084. For rays in a plane parallel to a and polarized in that plane p — 2'067. The optic axes lie in a plane parallel to a, and make angles of 4° 8 r with a normal to c. When seen in air through the faces c, they appear to make angles of about 8° 34' with a normal to c. Colourless, white, greyish, yellowish-white, lead-grey; sometimes green or blue from an admixture of carbonate of oxide of copper. Streak white. Father brittle, n = 3 - 6. g = 6-4...6-6. Decrepitates violently when heated. Before the blowpipe on charcoal becomes yellow, and is reduced. Soluble with effer vescence in nitric acid. The solution yields a precipitate with sulphuric acid. With hydrochloric acid a crystalline chloride of lead is produced. PbC, carbonic acid 16'47, oxide of lead 83'53. Analyses of cerussite a from Leadhills by Klaproth, b from Nertschinsk by John, c from Griesberg by Bergemann, d from Benkhausen near Allendorf by Schnabel: — a b c d Carbonic acid 16 io - 5 16'49 16'07 Oxide of lead 82 81‘4 83'61 83’93 Some varieties contain a very small quantity of carbonate of oxide of silver. A variety from Monte Poni in Sardinia, G = 6*9, contains 7'02 per cent, of carbonate of oxide of zinc. In crystals ; reniform, compact and earthy masses ; pseudo- morphous after galena, anglesite, leadhillite, baryte, fluor. Is found at Przibram, Mies and Bleistadt in Bohemia, Blei- berg in Carinthia, Bezbanya in Hungary, Zschopau and Johaun- Georgenstadt in Saxony, Zellerfeld and Clausthal in the Harz, Griesberg in the Eifel, Tamowitz in Silesia, Badenweiler in Baden, Miisen and Siegen in Westphalia, La Croix, Markirch, Huelgoiit and Poullaouen in France, Kiddensk in the Altai, Ildekansk, Taininsk, Nertschinsk and Kolywan in Siberia, Beeralston in Devonshire, St. Agnes in Cornwall, Alston Moor and Keswick in Cumberland, in Derbyshire, at Leadhills and * Wanlockhead in Scotland.