THE GENESIS OF THE DIAMOND. 207 



This composition shows tliat the roclc is extremely analogous to kimbeiiite ; 

 in fact, probably a subvariety of it. Zirkel considers kimberlite as closely allied 

 to Iherzolite, while Rosenbush appears uncertain how to classify it. 



Doctor Becker is still of the opinion that diamonds ought to be 

 found in the Iherzolite in spite of the result of the test of 20 tons. 



Quite a niunber of specimens of diamonds and garnets cemented 

 together have been found, but in most specimens which have come 

 under my observation the diamond has grown into the garnet. A 

 diamond was found (January 9, 1904) in Wesselton mine, Kimberley, 

 which had a small garnet embedded in it. The diamond weighed 

 114 carats, and the garnet w^as estimated to weigh about half a carat. 

 It appeared to fill the hole in which it was embedded. The diamond 

 was of cubic crystallization with nearly half of the cube wanting. 

 The part of the diamond in which the garnet was buried had numer- 

 ous depressions similar to the one containing the garnet, and one 

 is led to think that these depressions were also once filled with small 

 garnets, or, in other words, the diamond crystallized upon a nest of 

 garnets. It was of a peculiar plumbago color and semitransparent. 

 All of the diamonds crystallized in cubic form which have been 

 found of late in AYesselton^mine were of this peculiar color. Speci- 

 mens have also been found where the diamond was embedded in 

 olivine. 



5. .Sir William Crookes and others have mentioned diamonds which 

 burst or explode on being brought to the surface; and Sir William 

 says it has been '' conclusivel}^ proved that the diamond's genesis 

 must have taken place at great depths under enormous pressure. The 

 explosion of large diamonds on coming to the surface shows extreme 

 tension." 



Professor Lewis saj's that Kimberley diamonds have been found 

 sometimes to have optical anomalies due to strain. Fizzan thought 

 this strain to have been caused by the unequal distribution of heat 

 during cooling; but Jannettaz " holds that the strain is due to com- 

 pressed gas in the interior of the crystal. 



I have fomid that the light-brown smoky diamonds frequently 

 crack when brought from the mine to the surface; but even these 

 remain intact if kept in a moist place. In the days of open-cut work- 

 ing, when a smoky or light-brown diamond was found, the digger 

 placed it in his mouth, where he kept it until he offered it for sale. 

 The buyer placed it in a raw potato, in which it was shipped to 

 Europe. The temperature of the ground in which the stone was 

 found would, as a rule, not exceed 70° F. The temperature of the 

 diamond would be raised to 98° F. while in the digger's mouth. If, 

 however, the stone was kept in a dry place, even at a lower tempera- 



o Bulletin de la Societe Minerale de France, II, 1879, p. 124. 



