98 DIAMONDS AND 



it is much like broken chips of haematite ; of course, it is identi- 

 cal, chemically, with the crystalline Diamond, but excepting its 

 supreme hardness, it possesses little to remind one of a Diamond. 

 The Carbonate is found only in Brazil, and is much valued and 

 employed for engineering purposes, especially for rock-boring, for 

 which purpose it is preferable to the crystallised Diamond, being 

 less liable to spHt when subjected to great pressure or concussion. 



It would be impossible, in the limits of this paper, to describe 

 the various uses made of Bort and Carbonate, but their importance 

 will be indicated by the fact that selected pieces are mounted as 

 turning-tools for the turning of chilled steel rollers, emery-wheels, 

 stone, and such excessively hard substances as defy the finest 

 chisels that can be manufactured, thus avoiding, to a large extent, 

 the slow and laborious process of grinding by emery. It is also 

 mounted on rollers for the purpose of dressing mill-stones, and, 

 perhaps most important of all, it is made, as stated above, into drills 

 for rock-boring (see Plate). These drills are composed of a steel 

 ring, in the edge of which pieces of bort or carbon are embedded. 

 The ring is fastened on to the end of a steel tube, which is made 

 to revolve against the surface of the rock by steam power, and as 

 the drill grinds into the rock, it is lengthened by screwing fresh 

 steel tubes into the original one. Very deep borings (it is stated 

 over 2,000 feet) can thus be effected very rapidly. A good tool 

 will pierce hard granite at the rate of three inches per minute, 

 and so through many thousand feet, without serious wear 

 taking place. Of course, great pressure is required, and the Dia- 

 monds have to be kept cool by the pumping of water through the 

 tubes. The inferior kinds of Diamond are also crushed to make 

 diamond-powder, for which there is a very large and increasing 

 employment. 



The Diamond is usually described as crystallising in some 

 half-dozen separate and different forms. This is certainly inac- 

 curate, for, however dissimilar diamond-crystals may be in 

 appearance (and an almost infinite variety of very beautiful 

 and distinct forms occur), yet they are all reducible to the 

 simple normal form of the regular octahedron, from which 

 the most complex forms are built up according to a simple and 

 definite law. Nature would seem to have done her utmost to 



