360 EMIGRANT DIAMONDS IN AMERICA. 



most important feature of this alteration has been the recrystalization 

 of the carbon of the shale into diamond. 



This apparent explanation of the genesis of the diamond finds strong 

 support in the experiments of Moissan, who obtained artificial diamond 

 by dissolving carbon in molten iron and immersing the mass in cold 

 water until a firm surface crust had formed. The "chilled'' mass was 

 then removed, to allow its still molten core to solidify slowly. This 

 it does with the development of enormous pressures, because the nat- 

 ural expansion of the iron on passing into the solid condition is resisted 

 by the strong shell of "chilled" metal. The isolation of the diamond 

 was then accomplished by dissolving the iron in acid. 



The prevailing form of the South African diamonds is that of a 

 rounded crystal, with eight large and a number of minute faces — a 

 form called by crystallographers a "modified octahedron." Their 

 shapes would be roughly simulated by the pyramids of Egypt if they 

 could be seen, combined with their reflected images, in a placid lake, 

 or, better to meet the conditions of the country, in a desert mirage. 

 It is a peculiar property of diamond crystals to have convexly rounded 

 faces, so that the edges which separate the faces are not straight, but 

 gently curving. Less frequently in the African mines, but commonly 

 in some other regions, diamonds are bounded by 4, 12, 24, or even 48 

 faces. These must not, of course, be confused with the faces of cut 

 stones, which are the product of the lapidary's art. 



Geological conditions remarkably like those observed at the Kim- 

 berley mines have recently been discovered in Kentuck}^, with the 

 difference that here the shales contain a much smaller percentage of 

 carbon, which may be the reason that diamonds have not rewarded the 

 diligent search that has been made for them. 



Though now found in the greatest abundance in South Africa and 

 in Brazil, diamonds were formerly obtained from India, Borneo, and 

 from the Ural Mountains of Russia. The great stones of history 

 have, with hardly an exception, come from India, though in recent 

 years a number of diamond monsters have been found in South Africa. 

 One of these, the "Excelsior," weighed 970 carats, which is in excess 

 even of the supposed weight of the "Great Mogul." 



Occasionally diamonds have come to light in other regions than 

 those specified. The Piedmont plateau, at the southeastern base of 

 the Appalachians, has produced, in the region between southern Vir- 

 ginia and Georgia, some 10 or 12 diamonds, which have varied in 

 weight from those of 2 or 3 carats to the "Dewey" diamond, which 

 when found weighed over 23 carats. 



It is, however, in the territory about the Great Lakes that the 

 greatest interest now centers, for in this region a very interesting 

 problem of origin is being worked out. No less than 7 diamonds, 

 ranging in size from less than 4 to more than 21 carats, not to men- 



