

PHYSIOGRAPHY. 153 



Couzeranite. 



the yellow Oriental Topaz, and the blue Oriental Sapphire. Jlsteria 

 is a variety of Sapphire, not perfectly transparent, and shewing a star- 

 like opalescence in the direction of the axis, if cut in oval. Much use is 

 made of Corundum and Adamantine-Spar, particularly in India and Chi- 

 na, for cutting and polishing steel and gems, and it is said even of Dia- 

 mond, which has given occasion to the name of Adamantine-Spar. Em- 

 ery yields a well known polishing material. 



COTTUNITE. 



In acicular crystals. 

 Lustre adamantine, shining. 

 Color white. 



1. Before the blow-pipe, on charcoal, it melts very easily, coloring 

 the ilame blue, arid affords a white smoke, which adheres to the coal, 

 turns into greenish yellow flakes, and is chiefly converted into metallic 

 lead. Heated in a matrass, it melts and sublimes. It dissolves in wa- 

 ter ; and the nitrate of silver throws down from the solution, a precipitate 

 of chloride of silver. 



2. Analysis. 



Chlorine 25-48 



Lead . . . . . 74-52 



3. Its locality is believed to be Mount Vesuvius. 



4. Additional information is requisite before we can pronounce with 

 confidence as to* its specific rank. 



COUZERANITE. 



Primary form. Oblique rhombic prism. M on M = 96. 

 p on M = 92 or 93. 



Cleavage parallel with the shorter diagonal. 



Lustre vitreous. Color greyish black, black and indigo-blue. 



Hardness = 70. Sp. gr. = 26 . . . 2-7. 



1. Heated before the blow-pipe, it fuses into a white enamel. 



2. Analysis. 

 By DUFRESNOY. 



Silica 52-37 



Alumina 24-02 



Lime . 11-85 



Magnesia ..... 2-40 



Potash 5-52 



Soda 3-96 



