PHYSIOGRAPHY. 151 



Corundum. 



lucent. In several varieties, if cut round, a six-sided opa- 

 lescent star is observable in the direction of the axis. 

 Hardness 9-0. 

 Sp. gr. = 3-979, blue, transparent (Sapphire.) 



3-949, green, translucent (Corundum.) 

 3-921, brown, faintly translucent (Adamantine- 

 Spar.) 



3-909, red, transparent (Ruby.) 



Compound Varieties. Regular composition parallel to 

 one or more faces of P, repeated in parallel layers, very 

 frequent. Massive : composition granular, often impalpa- 

 ble, and then the fracture becomes splintery and uneven. 



1. Most of the transparent simple varieties have been designated Sap- 

 phire, while the compound ones have been called Emery. The varie- 

 ties of Sapphire, generally possess an indistinct cleavage, and a conchoi- 

 dal fracture; the surface of its crystals is smooth, though not always 

 even. The remaining varieties differ almost only in color, Corundum, 

 comprehending those whose color is green, blue or red, and in most ca- 

 ses inclining to grey, while those of Adamantine- Spar are hair-brown 

 and reddish-brown. Both of them are easily cleavable, or at least show 

 faces of composition parallel to the primary form ; and the crystals pos- 

 sess a rough and uneven surface, There are many crystals, part of 

 which is Sapphire and part Adamantine-Spar. 



Before the blow-pipe it is infusible, whether alone or with soda ; it is 

 with difficulty soluble in borax, and if previously reduced to powder, al- 

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

 2. Analysis. 



By KLAPROTH. By TENN ANT. 



Sapphire. Corundum. 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 . 0-00 . 0-00 



3. Corundum is found in imbedded crystals, and in massive varieties. 

 Sapphire is chiefly met with in the sands of rivers, and is accompanied 



