238 SYSTEMATIC DESCRIPTIOxN OF PRECIOUS STONES 



discovered by I. Friedlander. A small piece of olivine was fused in the gas-blowpipe and 

 the molten mass stirred with a rod of graphite. After cooling, those parts of the silicate 

 which had been in contact with the carbon were found to contain vast numbers of brown 

 crystals of microscopic size (O-OOl mm. in diameter). These crystals were found to be 

 octahedral or tetrahedral in form, to be unattacked by hydrofluoric and sulphuric acids, to 

 have a high refractive index, to sink slowly in methylene iodide, to burn away when heated 

 in a current of oxygen, and to be unaltered by heating in a current of carbon dioxide. All 

 these characters point to one conclusion, namely, that the crystals so produced are diamond, 

 and still further proof is furnished by the fact that the stony mass containing them is 

 capable of scratching corundum. 



When we essay to draw conclusions as to the origin of diamonds in nature from 

 experiments in their artificial production, we should be careful that the conditions of the 

 artificial production and of the natural occurrence are parallel. For exauiple, the 

 experiments of Moissan are most helpful in explaining the origin of diamond in meteoric 

 iron, while those of Friedlander suggest that the diamonds of South Africa and of meteoric 

 stones have been formed by the action of a molten silicate magma upon graphite or some 

 carbonaceous material. Friedlander himself suggests that, in the case of the South African 

 deposits, the carbon may have been derived from the carbonaceous shales which are 

 penetrated by the pipe of diamond-bearing " blue ground " ; there are, however, objections 

 to this view, as has been shown already. 



Further experiments in the artificial production of diamonds are desirable, especially 

 with a view to the discovery of a liquid capable of depositing carbon in the crystalline form 

 of diamond ; when more knowledge on this point has been obtained, it will, perhaps, be 

 possible to explain the origin of diamond in pegmatite veins and in itacolumite, as well as 

 in olivine-rock and in eclogite (p. 197). 



D. APPLICATIONS OF DIAMOND. 



The natural beauty of the diamond renders it primarily an object of jesthetic value ; 

 only faulty, opaque, or unpleasingly coloured specimens are applied to technical purposes 

 for which a material of great hardness is essential. 



1. APPLICATION IN JEWELLERY. 



The beauty of a diamond depends but rarely upon the tint of the pigment it may contain, 

 but is rather associated with the marvellous lustre and play of prismatic colours so 

 characteristic of this stone. This play of colour differs in degree in different stones, and 

 depends to a large extent on the method of cutting which has been adopted ; uncut stones, 

 with their rough, and often somewhat irregular faces, either do not show any play of 

 colours, or display it to only a very limited extent. 



How far the ancients were acquainted with the art of diamond-cutting, or even with 

 the polishing of the natural crystal-faces of the stone, is not certainly known, but that they 

 were not entirely ignorant of the process is apparent from their writings. 



In India, the ancient home of the diamond, the art of polishing the faces of natural 

 crystals was practised in the remotest times ; when or how the device of faceting stones 

 was discovered or introduced in this country is not known, but it was practised in the 

 seventeenth century, at the time of Tavernier's visit (1665). According to native ideas in 



