ORDER VII. RHOMBOHEDRAL CORUNDUM. 301 



a six-sided opalescent 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 (Ada- 

 mantine-spar). 

 3-909, red, transparent (Ruby). 



Compound Varieties. Regular composition pa- 

 rallel to one or more of the faces of R, repeated in 

 parallel layers, very frequent. Massive : composi- 

 tion granular, often impalpable, and then the frac- 

 ture becomes splintery and uneven. 



OBSERVATIONS. 



1. Among the varieties of rhombohedral Corundum, four 

 species used formerly to be distinguished, for the greater 

 part easily ascertained, but also united by such varieties 

 as possess intermediate properties between them, and 

 produce continuous transitions. By these transitions, how- 

 ever, also the Salamstone is included, which "WERNER. 

 considered as a sub-species of Spinelle, and which consists 

 of small transparent crystals, generally six-sided prisms, of 

 pale reddish and blueish colours. Most of the transparent 

 simple varieties, however, were designated by the name 

 of Sapphire, while the compound ones were called Emery. 

 The varieties of Sapphire generally possess an indistinct 

 cleavage and a conchoidal fracture; the surface of its 

 crystals is smooth, though not always even. The re- 

 maining varieties differ almost only in colour, Corundum 9 - 



The corundum of Battagammana is frequently found in 

 large six-sided prisms; it is commonly of a brown colour, 

 whence it is called by the natives " Curundu galle," cinnamon- 



