\L 



PHYSIOGRAPHY. 167 



Diamond. 



and even black. Generally pale. Streak white. Trans- 

 parent . . . translucent, dark colored varieties only on their 

 edges. If cut and polished, it shows a most lively play of 

 color. 



Hardness =10*0. Sp. gr. = 3*520, of a white variety. 



Compound Varieties. Twin-crystals. Axis of revolu- 

 tion perpendicular to a face of the octahedron ; angle of 

 revolution =60. (See fig. 50.) Also-, axis of revolution 

 parallel to one of the axes of the rhombic dodecahedron 

 which passes through the obtuse solid angles. (See the 

 annexed figure.) Angle of revolution =60. 



Fig. 159. 



1. Diamond is perfectly combustible at a temperature of about 14 

 Wedgewood, and yields with oxygen, carbonic acid gas. His not acted 

 iipon by acids or alkalies. 



2. The rocks hitherto considered as the gangue of Diamond are secon- 

 dary ones, as several kinds of sandstone, consisting of aggiegated quartz 

 pebbles. It Is also found in strata of iron-shot sand and clay, and in the 

 loose sand of plains and rivers. In a specimen from Brazil, in the pos- 

 session of Mr. HEULAND, it is associated with Skorodite, and imbedded 

 in a compact variety of Brown Iron-Ore. 



8. The Diamond was first discovered in the East Indies, where it ha 

 been worked for many centuries, and in Brazil. They are found in va- 

 rious places on the eastern coast of the British peninsula in India, btit 

 particularly between Golconda and Masulipatam ; also near Panna in 

 Buodelcund, It also occurs in the peninsula of Malacca, and the isle of 





