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TRIPOLI. 427 It occurs massive. It is dull. The fracture is coarse earthy, inclining to slaty. The fragments are angular. It is very soft, passing into friable. It feels meagre, and rather rough. It does not adhere to the tongue. Specific gravity, 2.202, Bucholz. Chemical Characters. It is infusible before the blowpipe. Constituent Parts. Silica, - Alumina, Trace of Lime. Black and Red Oxide of Iron, Sulphuric Acid, Water, - * Loss, - The sulphuric acid and water are dental constituent parts. Gecgnoslic Situation. It occurs in beds in coal-fields; also in beds, along with floetz limestone, and alternating with clay, under basalt. Geographic Situation. It is found in Derbyshire, where it is named Rotten- stone; also in the coal-fields of Dresden and Thuringia; in flcetz-trap districts in Bohemia; in Auvergne, where it 81.00 150 8.00 3.45 4.55 1.50 100 Bucholz. considered as acci-