200 THE GENESIS OF THE DIAMOND. 



Large sheets of calcite are frequently found at the junction of these 

 rocks, which have taken the form of the stria?. Beautiful calcite 

 crystals and transparent pieces of doubly refracting, or Iceland spar, 

 are of frequent occurrence. 



There is conclusive proof that the diamonds in the South African 

 mines are not found in their original place of crystallization, as is 

 shown by the frequent occurrence of broken crystals embedded in 

 the hard kimberlite. The geological strata of the rocks which sur- 

 round the diamond-bearing pipes of the Kimberley district are shown 

 in figure ti. 



Concerning the discussion of the genesis of the diamond. Sir Isaac 

 Newton's oj^inion was that it was of vegetable origin and combusti- 

 ble; but it was not until 1694 that the combustibility of the diamond 

 was actually proved by the famous burning-glass experiment of 

 the academicians of Cimento. 



Lavoisier, Guyton de Morveau, and others determined that the 

 diamond was converted into carbonic dioxide by burning. The 

 experiments of Sir Humphry Davy, in 1810, showed that the dia- 

 mond was almost pure carbon. These experiments have been con- 

 firmed by Dumas, Stas, Friedel, Roscoe, and other eminent chemists, 

 who have fixed with extreme precision the composition of the dia- 

 mond to be pure carbon in crystalline form. The late Dr. W. Guybon 

 Atherstone was one of the first scientists to deal with the occurrence 

 and genesis of the diamond in the Kimberley mines. Being a resi- 

 dent of the Cape Colony, he made frequent visits to the diamond 

 fields and made personal investigations." 



"For a substance to crystallize," he says, 'its molecules nuist be 

 free to move. * * * The diamond, we know, is neither soluble 

 nor fusible. It is the element carbon crystallized, and is consumed by 

 heat. How, then, could it survive as a crystal in the center of a vol- 

 cano? The key to solve this mystery was placed in my hands over 

 half a century ago by one of the greatest philosophers of the age, 

 whose lectures I had the privilege of attending. * * * ' Hold out 

 your hand,' said Faraday, at the close of the lecture that fairly elec- 

 trified the world of science, as with a loud hiss a snowy substance, 

 burning like a coal, but in reality intensel}^ cold, escaped into the 

 palm of my hand from the strong iron vessel, in which, with a pres- 

 sure of fifty atmospheres, he had liquified carbonic acid gas — the very 

 gas resulting from the combustion of the diamond. * * * In the 

 carbonic acid gas generated from the carbonaceous shales by heat 

 and interspersed as gas bubbles in the cavities of the viscid, ferrugi- 

 nous amygdaloid and in the admixture of steam, lava, and ashes known 

 as the 'Kimberley blue,' reduced to the liquid state by the enormous 



"Geological Magazine, Vol. VI. p. 208, May, 1889. 



