24 MINERALOGY. 



by burning it in oxygen gas, the product being carbonic 

 acid gas, a compound of carbon and oxygen, just as in 

 the burning of charcoal. As in pure charcoal and an- 

 thracite we have carbon alone, the diamond differs from 

 them merely in the arrangement of the atoms. It is this 

 alone that causes the immense difference in characteris- 

 tics. When the diamond is colored, as it sometimes is, 

 there is coloring matter intimately mingled with the car- 

 bon, as glass is colored with something added to it. But 

 the quantity of coloring matter is so exceedingly minute 

 that it could not be detected unless a considerable amount 

 of diamond were burned, an experiment so expensive that 

 I presume that it never has been tried. 



31. Qualities of the Diamond. It is the hardest of all 

 substances. Its lustre is peculiar ; and other gems that 

 are similar to it in this respect are said to have an ada- 

 mantine lustre. Its reflection of light is exceedingly 

 brilliant. It is commonly colorless, but sometimes red, 

 yellowish, orange, green, or black. The rose diamond is 

 highly valued for the beauty of its color, and so also is 

 the green diamond. The black diamond is very rare, 

 and therefore commands a high price, although it has no 

 beautj* 



32. Size of Diamonds. In speaking of the size of dia- 

 monds the term carat is used. This is the name of a 

 bean, which was used in its dried state by the natives of 

 Africa in weighing gold, and in India in weighing dia- 

 monds. Though the bean is not used for this purpose 

 now, the name is retained, and the carat is nearly four 

 grains Troy. The largest diamond known is in the pos- 

 session of the Great Mogul. It weighed originally 900 

 carats, or 2769 grains, but it was reduced by cutting to 

 861 grains. It is of the size of half a hen's egg, and is in 

 that form. The Pitt or Regent diamond weighs 419 

 grains. The famous Koh-i-noor weighed originally 186 

 carats, but was reduced by recutting one third. 



33. Cost of Diamonds. The cost of diamonds depends 



