MANUAL OF NATURAL HISTORY. 619 



Diamond, octahedral or dodecahedral, H. = 

 10, sp. gr. =3'5, white, or at times variously 

 tinted ; found in beds of streams, with sand 

 and quartz pebbles, often with gold and 

 platinum ; 2, Mineral coal, H. = 1 2'5, sp. 

 gr. = 1 -2 1 75, black or brown, opaque, 

 brittle or sectile ; sometimes with a small 

 proportion of silica, alumina, oxide of iron, or 

 bitumen ; divided into bituminous and non- 

 bituminous, the forming being the more 

 abundant and valuable, comprising all the 

 commercial varieties ; 3, as Carbonate of Iron 

 or " Graphite/' or " Black Lead/' hexagonal, 

 H. 1 2, sp. gr. 2 2 -3, dark steel-gray, 

 sectile, greasy, soils paper, in gneiss, mica- 

 slate, and primitive-limestone ; 4, combined 

 with oxygen or "Carbonic acid/' sp. gr. 

 1 *524, contained in many springs, and 

 evolved from some volcanoes ; also with 

 bases forming " Carbonates." Symb. C. 

 2. FAMILY. Halicides. Minerals containing com- 

 pounds of Silicon. Occur 1, with oxygen 

 as "Silica/' rhombohedral, H. = 7, sp. gr. = 

 2*6, forms three varieties, 1, the vitreous or 

 "Quartz," or "Rock-crystal," when tinted 

 purple by oxide of iron, it is "Amethyst/' 

 when smoky-brown it is " Cairngorm-stone /' 

 2, the sub-vitreous, or " Chalcedony," or 

 " Flint," when coloured with oxide of iron 

 it is "Carnelian," when variegated, "Agate," 

 or "Onyx;" 3, the dull, or "Jasper," when 



