302 PHYSIOGRAPHY. CLASS II. 



stone comprehending those whose colour is green, blue, 

 or red, and in most cases inclining to grey, while those 

 of Adamantine -spar are hair-brown and reddish-brown. Both 

 of them are easily cleavable, or at least shew faces of com- 

 position parallel to the fundamental rhombohedron, and the 

 crystals possess a rough and uneven surface. There are 

 many crystals, part of which is Sapphire, and part Ada- 

 mantine-spar. 



3. The following ingredients have been found in rhom- 

 bohedral Corundum : 



Sapphire. Corundum-stone, Emery. 

 Alumina 98-50 89-50 86-00. 



Silica 0-00 5-50 3-00. 



Oxide of Iron 1-00 1-25 4-00. 



Lime 0-50 KLAPR. 0-00 KLAPR. 0-00. TENNANT. 



Its chemical formula is Al, expressing 53-29 of aluminium, 

 and 46-71 of oxygen. Before the blowpipe it is infusible 

 whether alone or with soda ; it is difficultly but entirely dis- 

 solved in borax, and if previously reduced to powder, also 

 in salt of phosphorus. It is not acted upon by acids. 



3. Rhombohedral Corundum is found in imbedded crys- 

 tals and in massive varieties. The first of them, and par- 

 ticularly Sapphire and Salamstone, are chiefly met with in se- 

 condary repositories, as in the sand of rivers, &c. and is ac- 

 companied by crystals and grains of octahedral Iron-ore, and 

 of several species of gems. Corundum-stone is found in 

 imbedded crystals in a rock, which consists, according to 

 Count BOURNON, of Indianite, and contains Felspar, Fib- 

 rolite, several species of Augite-spar and Gem, and also 

 octahedral Iron-ore. Adamantine-spar occurs with octahe- 

 dral Iron-ore and Fibrolite in a sort of granite, containing 

 no quartz. The varieties from Piedmont are imbedded in 



stone. Dr J. DAVY'S Account of the Interior of Ceylon, p. 25. 

 Dr DAVY adds, that the corundum and sapphire are so 

 closely allied, that even the natives of Ceylon have not failed 

 to observe the connexion, H. 



