234 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



was accepted also by the Scotch mineralogist, Jameson, and similar views were held by 

 Petzholdt. 



D'Orbigny regarded the diamond as a decomposition product of extinct plants ; the 

 same view was held by Wcihler, who assumed the alteration to have taken place at a low 

 temperature, and vigorously disputed the theory which demanded a high temperature for the 

 formation of the diamond. J. D. Dana, on the other hand, regarded a high temperature if not 

 as an essential, at least as a probable condition, and considered that the diamond might have 

 been derived from organic substances by the same processes which effect the metamorphism 

 of rocks. Goppert entertained similar views, owing to his belief that in the course of his 

 detailed investigation of the enclosures of diamond he had detected plant remains. By 

 theorists of this school it was supposed that the decomposition products of decaying vegetable 

 gradually escaped, leaving behind a substance which contained an ever-increasing proportion 

 of carbon ; this substance, having been at length transformed into pure, amorphous carbon, 

 was supposed to be capable of taking on the crystalline form of diamond. Very similar 

 views were held by G. Wilson, who supposed that hydrogen and oxygen gradually escaped 

 from woody matter and left behind a substance resembling anthracite, which, by further 

 alteration, he conceived might be transformed into diamond. These processes were assumed 

 to take place at a low temperature, since at higher temperatures graphite, and not diamond, 

 would be formed. 



The opposite opinion was held by Parrot, namely, that the alteration of woody matter 

 took place at high temperatures ; he suggested that the transformation into diamond of 

 small particles of carbonaceous matter, strongly heated by volcanic agencies, was effected by 

 a sudden cooling. Carvill Lewis has expressed similar views with special reference to the 

 origin of South African diamonds. He considered the diamond to be formed in the 

 kimberlite at the time this was erupted into the pipes as a molten igneous rock. Numerous 

 fragments of the carbonaceous and bituminous shales, through which the igneous rock forced 

 a passage, were caught up by the igneous mass, and Carvill Lewis supposed the heat of this 

 mass to have converted the carbon contained in the fragments of shale into diamond. 

 According to the views of other investigators the igneous rock itself contained carbon, which 

 crystallised out of the molten mass as diamond , before it was erupted into the volcanic pipes. 



C. C. von Leonhard also invoked the aid of volcanic heat, but supposed the carbon to 

 be volatilised, and diamonds to be formed by the crystallisation of the sublimed carbon. 

 G. Bischof, while he does not combat the view that the diamond has been formed from 

 vegetable matter, makes no definite statement with regard to its mode of origin other than 

 the opinion that a high temperature is an impossible condition. 



Liebig supposed that by some kind of decomposition a product growing ever richer in 

 carbon was separated out from a fluid hydrocarbon, and that this product, when it finally 

 became pure carbon, crystallised in the form of diamond ; he pointed out that such a mode 

 of origin could only conceivably take place at low temperatures, the combustibility of the 

 substance i-endering the process impossible under the conditions of a high temperature and 

 the presence of oxygen. Berthelot, though not referring specially to diamond, has asserted 

 that a separation of carbon from such a liquid could take place only under the influence of 

 heat, a statement directly opposed to the assumption made by Liebig. Chancourtois 

 brought forward a theory to the effect that diamond has been formed by the slow oxidation 

 of emanations of a gaseous hydrocarbon, the hydrogen forming water, part of the carbon 

 forming carbon dioxide, and the remainder crystallising as diamond, the whole process being 

 analogous to the formation of sulphur from hydrogen sulphide, the oxidation of the hydrogen 

 being accompanied by the separation of crystals of sulphur. 



