

1 873.] New Facts concerning the Diamond. 439 



time it was only known and sought for in that form. At 

 present, equal attention is paid to irregular fragments of a 

 blackish or greyish colour, occasionally of considerable size, 

 also yielded by the washings of diamandiferous sand, which 

 formerly passed unregarded. These fragments are now 

 carefully collected, and have acquired some considerable 

 value in commerce, where they are known under the name 

 of carbonado or carbon. Their aspect is generally that of a 

 rounded mass (although they are sometimes angular) 

 blackish in colour, and presenting a shiny surface as if 

 polished by rubbing. When split, however, their appear- 

 ance is dull, relieved here and there by a brilliant speck, 

 numerous pores of unequal dimensions being perceptible 

 with a lens. The colour of the split surface varies, being 

 sometimes greyish and sometimes violet. Upon heating in 

 water, considerable evolution of gaseous bubbles ensues ; it 

 is therefore necessary, when ascertaining their specific 

 gravity, to boil the fragments for some time in water, to 

 liberate as much as possible the air contained in their pores. 

 Upon treatment with aqua regia the solution was found to 

 contain a considerable quantity of iron and a small portion 

 of lime, but no traces of either sulphuric acid or alumina 

 were to be found. Combustion in oxygen produced a small 

 quantity of ash from 0*24 to 2 per cent, according to Rivot. 

 It is to be hoped that carbonado may be subjected at some 

 future time to a more minute examination. 



Although quite unadapted to ornamental purposes, owing 

 to its appearance, which is totally dissimilar to that of the 

 diamond, carbonado cannot be considered as constituting an 

 essentially different condition. Upon examining large 

 quantities of carbonado and of diamonds, it is often difficult 

 to decide whether certain specimens should be placed in the 

 category of carbonado, which presents no appearance of 

 crystalline structure when seen by the naked eye, or in that 

 of dark diamonds of incomplete and irregular crystallisation. 

 An examination of these numerous varieties has made it 

 evident that between carbonado of a simply micro-crystalline 

 texture, and the diamond regularly crystallised in dia- 

 phanous octahedrons, there exists an uninterrupted series 

 of intermediate conditions. The true diamond will cleave 

 in a direction parallel with the facets of the octahedrons, 

 while pure fine-grained carbonado possesses no such quality, 

 which may nevertheless be found in various degrees 

 amongst the intermediate varieties. It is a remarkable 

 fact that carbonado, which in Brazil, and especially in 

 Bahia, always accompanies the diamond, in fragments 



