118 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



distribution of impurities through the whole mass of the crystal is occasionally shown by the 

 incombustible residue remaining behind as a porous mass, and having the form of the 

 original diamond crystal. 



The ash of the diamond is of a brownish colour. It contains some yellow flakes, and 

 sometimes a few black grains which are attracted by a magnet. Its precise character 

 depends, of course, upon the nature of the impurity in the diamond. Occasionally a few 

 small, transparent, crystalline grains are present in the ash which have an action on 

 polarised light ; these and kindred impurities require a microscope for their detection. 

 Chemical examinations of the ash of diamonds show that silica and iron oxide are invariable 

 constituents, while lime and magnesia appear also in certain cases. An analysis of the ash 

 of carbonado has given : silica 33-1 per cent., iron oxide 53-3, lime 13-2, and a trace of 

 magnesia. 



The constituents of the ash of diamond are, as a rule, very finely divided and distributed 

 throughout the mass of the stone, the individual particles of the impurity not being 

 recognisable even under the strongest magnification. Particles of foreign matter are some- 

 times, however, large enough to be seen with a lens or even with the naked eye ; these 

 bodies, which are referred to as enclosures, are isolated grains, splinters, scales, plates, 

 needles, or fibres. They have definite sharp boundaries, and not infrequently are bounded 

 by plane crystal-faces ; they may occur in the diamond singly or in groups. 



The nature and character of large enclosures is sometimes definitely known, but more 

 frequently this is not the case. A peculiar and rare occurrence is the enclosure of a small 

 diamond within a larger one, the two sometimes differing from each other both in crystalline 

 form and in colour. In some cases the smaller enclosed diamond is quite free from the 

 larger stone, and when the latter is cleaved open, the small enclosed stone falls out 

 uninjured and perfect. The most commonly occurring enclosures in diamond are small 

 black grains of irregular outline ; they occur in large numbers in diamonds from all 

 localities, and were formerly considered to consist of some carbonaceous substance. This, 

 however, is not always the case. The black enclosures found in a diamond from South 

 Africa by E. Cohen had the characters of haematite or ilmenite, and he is inclined to the 

 opinion that all such enclosures consist of one or other of these two minerals. Many of 

 these black grains are incombustible, and therefore inorganic ; but others, according to the 

 observations of Friedel, are consumed with the diamond, and hence must consist of some 

 carbonaceous substance. In a diamond from the Cape a black, viscous, asphalt-like mass 

 has been found, and similar enclosures have been reported in a few Indian crystals. Beside 

 the minerals already named, several others have been determined with more or less certainty 

 to occur as enclosures in diamond; these include, among others, quartz, topaz, rutile, 

 iron-pyrites, which occur in the form of irregular grains or sometimes as well-developed 

 crystals. Scales of gold have been found, though rarely, as enclosures in diamond crystals 

 from Brazil. Vermiform aggregates of green scales are sometimes observed ; these, however, 

 are differently Interpreted by different observers : Des Cloizeaux considers them to be a 

 kind of chlorite, while Cohen regards the green scales in Cape diamonds as some copper 

 compound. Red enclosures are very occasionally met with in Cape diamonds ; they are of 

 unknown nature. 



Special mention must be made of enclosures of very fine green needles and fibres 

 interwoven and matted into coil-like masses. In these and in aggregates of a similar kind, 

 the structure of plant cells has sometimes been supposed to have been recognised ; the 

 distinguished botanist, Goppert, indeed, held that such enclosures were undoubtedly of a 

 vegetable nature. It has since been proved, however, that they consist of inorganic 



