

CHAPTER IV 

 THE NATIVE ELEMENTS 



DIAMOND 



Diamond. Carbon, C; Isometric; Type, Ditesseral Polar; 

 Common form, o (111); Twinning planes, 111 and 100; Cleavage 

 octahedral, perfect; Brittle; Fracture, conchoidal; H. = 10; 

 G. = 3.51 3.52; Color, white, yellow, brown to black, rarely blue 

 or green; Luster, adamantine to slightly greasy; Transparent 

 to opaque; n = 2.42; Dispersion strong =.063. 



B.B. Infusible, insoluble in acids. When heated tg a high 

 temperature for a long time it burns slowly, forming CO 2 . 

 Colored stones may change color on heating. 



General description. Always crystalline, usually simple octa- 

 hedrons or rounded hexoctahedrons which are supplementary 

 twins, combinations of the plus and minus hextetrahedrons, in 

 which the octahedral edge- is replaced by a reentrant angle. 

 Simple tetrahedral forms and the cube are rare. Crystal faces are 

 often drusy or covered with triangular etch-figures, due to corro- 

 sion, which is also the cause of the rounded appearance of many 

 diamond crystals. Twins after the spinel law, where the face of 

 the octahedron is the composition plane, are not uncommon. 



The perfect octahedral cleavage is utilized by the cutters in the 

 rough preparation of the stones for the grinders. While the 

 diamond is the hardest known substance, it is brittle and easily 

 broken or ground to powder, the dust of which is used on the 

 wheels or " skeifs " in grinding and polishing the facets of the cut 

 stone. The inclination of all facets of the brilliant is calculated 

 so that the greatest amount of light is totally reflected and 

 returned. Owing to the high index of refraction, rays which 

 meet the lower facets at an angle greater than 24 13' are inter- 

 nally totally reflected, and emerge above the girdle, owing to the 

 very strong dispersion, yielding prismatic color. The high index 

 of refraction and strong dispersion are the two properties which 



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