MANUAL OF NATUKAL HISTORY. 609 



or earthy, brown, in crystalline and second- 

 ary rocks ; 3, " Magnetic Iron Ore/' octahe- 

 dral or dodecahedral, sp. gr. 4*9-5*2, H. = 5*5- 

 6*5 , metallic or sub-metallic, iron-black, mag- 

 netic ; 5, as Chromate, in octohedrons, sp. gr. 

 4-3, EL = 5*5, sub-metallic, brown, sometimes 

 magnetic, in serpentine ; 6, with Silica, Mag- 

 nesia and Alumina, as " Green-Earth ;" 7, as 

 Carbonate or " Spathic-Iron/' rhombohedral, 

 sp. gr. 3 7, H. = 3*5-4-5, grayish, brittle, in 

 gneiss, mica and clay-slate, and in coal strata ; 

 8, as Sulphate or " Green Vitriol/' in oblique 

 rhombic prisms, sp. gr. 1*8, H. = 2, green, so- 

 luble, taste inky, from decomposition of "Xron- 

 pyrites ;" 9, as Phosphate or " Vivianite/' in 

 oblique prisms, sp. gr. 2-6, H. = 1*5-2, blue or 

 green, sectile. Salts of protoxide of iron give 

 a bluish-white precipitate with solution of 

 ferrocyanide of potassium (prussiate of po- 

 tassa), and a deep blue with the ferricyanide 

 (red prussiate of potassa) ; salts of the per- 

 oxide give a deep blue precipitate with the 

 ferrocyanide ; with borax iron salts form a 

 dark red glass in the oxidizing flame, becom- 

 ing yellow in the reducing flame. Symb. Fe. 

 10. Family. — Chromiides. Minerals containing 

 compounds of chromium. Occur 1, as Sul- 

 phuret or " Shepardite/' in meteoric stones, 

 prismatic, H. = 4, brownish-black ; 2, as Hy- 

 drous-Silicate or " Wolckonskoite/' amor- 

 phous, greenish, resinous, fragile ; 3, with 



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