GUIDE TO THE MIXERALOGIC COLLECTIONS 47 



PART 2 

 DESCRIPTION OF MINERAL SPECIES 



NATIVE ELEMENTS 



Native elements are divided into two groups, metals and non- 

 metals; between these two is inserted a series of semimetals 

 which partake, sometimes of the nature of the metals and some- 

 times of the nature of the nonmetals. 



XONMETALS 

 Diamond, carbon C 



Diamonds are usually found in isolated, rounded, isometric 

 crystals, octahedrons or modified octahedrons (pi. 12J. They are 

 transparent, with an adamantine luster, like oiled glass, and 

 are commonly colorless or faintly tinted. 



The diamond is the hardest substance known; this, together 

 with its high refractive power and easy octahedral cleavage, 

 renders it particularly suited for a gem stone, while the com- 

 parative rarity of unflawed crystals and the difficulty expe- 

 rienced in cutting them owing to their extreme hardness, com- 

 bine to make diamonds objects of considerable value. .Massive 

 and impure varieties are used for abrasive materials and in such 

 cutting machinery and tools as require very hard edges. These 

 massive varieties are known as bort and carbonado. Bort con- 

 sisis of rounded forms of confused crystalline structure. Car- 

 bonado is a black, massive form without cleavage. 



Diamonds occur chiefly in alluvial deposits of gravel, sand or 

 clay, the associated minerals being those common to granitic 

 rocks. Diamonds were formerly extensively obtained from 

 India, which has produced many remarkable gems; later they 

 were discovered in Brazil, but the present great diamond pro- 

 ducing region is Smith Africa. 



Graphite, carbon C 



Like the diamond, graphite is composed <>f carbon sometimes 

 containing iron, clay, sand or other impurities, h occurs in sofi 

 black Hakes <>r scales which are rarely hexagonal in shape. 



