298 PHYSIOGRAPHY. CLASS 11. 



species are highly prized as ornamental stones. They go 

 generally by the name of Spindle lluhy, or Balas Ruby. 



%. OCTAHEDRAL CORUNDUM. 



Octahedral Corundum, first subsp. JAM. Syst. Vol. I. p. 

 39. Octahedral Corundum or Automalite. Man. p. 

 184. Automalite. PHILL. p. 83. Automolit. WERN. 

 Hoffm. H. B. I. S. 526. Gahnit. HAUSM. II. S. 364. 

 Gahnit. LEONH. S. 513. Spinelle zincifere. HAUY. 

 Tabl. comp. p. 67. Traite^ 2de Ed. T. II. p. 170. 



Fundamental form. Hexahedron. Vol. I. Fig. 1. 

 Simple form. 6 (P). Vol. I. Fig. 2. 



Cleavage, octahedron, perfect. Fracture conchoi- 

 dal. Surface rough, sometimes covered with mi- 

 ca, or with dodecahedral Garnet-blende. 



Lustre vitreous, inclining to resinous. Colour 

 dirty green tinges, inclining to black and blue. 

 Streak white. Translucent on the edges ... 

 nearly opake. 



Hardness = 8-0. Sp. Gr. 4-232. 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpendi- 

 cular to a face of the octahedron. Fig. 156. 



OBSERVATIONS. 



1. Octahedral Corundum consists, according to ECKE- 



BERG, Of 



Alumina 60-00. 



Oxide of Zinc 24-25. 



Oxide of Iron 9-25. 



Silica 4-75. 



with a trace of oxide of manganese and lime. The pure 

 mixture is considered by BERZELIUS to be expressed by 



