DIAMOND: OCCURRENCE IN BRAZIL 175 



The hardness of carbonado not only equals that of diamond, but may even exceed it, 

 and its hardness is supposed to be greater the less distinctly it is crystalline. Carbonado 

 cannot therefore be cut by ordinary diamond powder, or at least only with extreme difficulty ; 

 it forms a valuable cutting material for ordinary diamonds, and large quantities are used as 

 a grinding material for this and other purposes which require exceptionally hard material. 

 On account of its great hardness, combined with the . absence of cleavage (in the mass), 

 carbonado is specially suitable for the rock-drills of boring machinery ; moreover, it possesses 

 another advantage over the diamond in that it can be easily shaped into any required form 

 and size, while with ordinary diamond either a natural crystal or a cleavage fragment must 

 be used. 



The specific gravity of carbonado is, on account of its porous nature, lower than that 

 of diamond crystals. The values 3-012, S'l^l, 3-255, 3-416, &c., have been determined; 

 the last three of these values were determined with the three specimens of which the 

 chemical composition is given above, and in the same order. Carbonado, when reduced to 

 powder, has of course the same specific gravity as ordinary diamond. 



That the occurrence of carbonado is almost entirely confined to the district of the 

 Serra da Cincora has already been mentioned. It was found for the first time in the year 

 1843 in the " gupiarras " of the river San Jose, and all the carbonado required for technical 

 purposes is derived from this source. In Minas Geraes carbonado may be said to be 

 completely absent ; in South Africa it is present in very small amount ; and in India and 

 Australia no trace of it has been met with. In the diamond sands of Borneo it is less rare, 

 and here are to be found nodules of carbonado enclosed by a shell of colourless diamond. 

 In every locality in which it occurs this black, porous variety of diamond is associated with 

 crystals of the usual kind, they are found in the same rocks, and have no doubt a common 

 origin and mode of formation. 



The production of carbonado in the Serra da Cincora, which in former times was 

 considerable, has now appreciably diminished, being scarcely more than 350 grams per 

 month. This, and its ever increasing application for technical purposes, has caused a 

 tremendous rise in price. When first found little use was made of it, and it could be 

 bought for about 2|(i. per gram ; now, however, for ordinary qualities the same weight 

 costs S2s. and the better qualities 80*., and the price shows a tendency to rise still 

 higher. 



Diamonds in considerable numbers have also been found in the southern part of the 

 State of Bahia, near the border of Minas Geraes. This district may be regarded as a 

 continuation in a north-easterly direction through Grao Mogol of the diamond-fields of 

 Diamantina. The stones are found near Salobro (signifying brackish) in the alluvial 

 deposits of the Rio Pardo. This river and the diamantiferous river Jequetinhonha (Rio 

 Belmonte) both empty themselves into the Atlantic Ocean at the foot of the Serra do Mar 

 and near the small haven of Canavieiras. The mines are about two days' journey inland 

 from this seaport town, and from it they derive their name of the Canavieiras mines. 



The discovery of diamonds here was made in 1881 or 1882 by a forester who had 

 previously searched for diamonds in other districts. Scarcely was the occurrence made 

 known, when the virgin forest, in spite of the unhealthy malarial climate, became peopled 

 by 3000 or more diamond miners. The treasure was obtained at a depth of two feet below 

 a white clay containing decomposing vegetable matter, so that the deposit is a very recent 

 one. The diamantiferous stratum is much more clayey than any in Minas Geraes ; it has 

 throughout the character of a plateau-deposit. Diamonds are also found in the rivers 

 Salobro and Salobrinho, tributaries of the Rio Pardo, especially in the "gupiarras" or 



