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. ‘T'rans- 
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. 
Inf. 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 
bort, 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.=8 to 3:42. Another kind is 
much like anthracite, G.=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, 
