CARBON GROUP. 103 



with more or less of hydrogen and oxygen and usually some 

 nitrogen. 



Diamond. 



Isometric. In octahedrons, dodecahedrons and more com- 

 plex forms. Faces often curved, as in the figures. Cleavage 

 octahedral ; perfect. 



Color white, or colorless ; also yellowish, red, orange, 

 green, blue, brown or black. Lustre adamantine. Trans* 

 parent; translucent when dark - colored. H. =10. G-. = 

 3.48—3-55. 



Composition. Pure carbon. It burns and is consumed at 

 a high temperature, producing carbonic acid gas. Exhibits 

 vitreous electricity when rubbed. Some specimens exposed 

 to the sun for a while, give out light when carried to a dark 

 place. Strongly refracts and disperses light. 



Biff. Diamonds are distinguished by their superior hard- 

 ness ; their brilliant reflection of light and adamantine 

 lustre, their vitreous electricity when rubbed, which is not 

 afforded by other gems unless they are polished ; and, by the 

 practiced ear, by means of the sound when rubbed together, 



Obs. The coarse diamonds, unfit for jewelry, are called 

 tort, and the kind in black pebbles, or masses, from Brazil, 

 carbonado. The latter occur sometimes in pieces 1,000 

 carats in weight ; they have G. =3 to 3*42. Another kind is 

 much like anthracite, Gr. =1 -66, although as hard as diamond 

 crystals ; it is in globules or mammillary masses, often partly 

 made up of concentric layers. 



Diamonds occur in India, in the district between Golconda 

 and Masulipatam, and near Parma, in Bundelcund, where 

 some of the largest have been found ; also on the Mahanuddy, 



