176 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



valley-deposits lying above the present high-water level, just as in the valleys about 

 Diamantina. 



The minerals associated with the diamond in these clays are not only less in amount 

 but also differ in kind to a certain extent from those found in Minas Geraes. Monazite in 

 yellowish and reddish broken crystal fragments is present in abundance, also zircon, usually 

 brownish to white in colour, but sometimes violet, and in addition kyanite, staurolite, 

 almandine, hfematite, ilmenite, magnetite, iron-pyrites, and a somewhat considerable amount 

 of corundum. The occurrence of corundum is remarkable, as hitherto it has been found in no 

 other Brazilian deposit, while all the other minerals mentioned do occur in association with 

 diamond in various parts of Brazil. We may contrast with the occurrence here of corundum 

 the complete absence of certain minerals, which in other parts of Brazil are frequently found 

 with diamond, namely, rutile, anatase, tourmaline, and the hydro-phosphates. 



As regards the origin of the diamonds found here, it has been supposed that they are 

 derived from the gneiss, granite, and other ancient crystalline rocks of the neighbouring 

 coast range, the Serra do Mar. In the diamantiferous deposit, however, there is no trace of 

 felspar or mica, two essential constituents of these rocks ; moreover, the minerals chrysoberyl, 

 andalusite, tourmaline, beryl, &c., which are frequently present in such rocks in Brazil, are 

 also conspicuous by their absence from these deposits, so that this suggested origin for the 

 diamond seems decidedly doubtful. For a satisfactory determination of the mother-rock of 

 these diamonds, further investigation is required ; in any case, it does not seem to be 

 itacolumite, since this rock has not been observed in any part of the surrounding district. 



Immediately after their discovery, the yield of these mines was so abundant that other 

 diamond districts became more or less deserted. The stones are distinguished by great 

 purity and freedom from colour, as well as by their very regular octahedral form, which 

 obviates any necessity for preliminary cleaving, and enables them to be cut at once. For a 

 time these mines supplied a large proportion of the total Brazilian output ; they may not, 

 however, have been as rich as they appeared, for it has been asserted that many Cape 

 diamonds were sent to Canavieiras in order to be put on the market as Brazilian stones and 

 so command a higher price, just as in former times Brazilian stones were shipped to India 

 to enter the market as Indian stones. At the present time the yield, compared with what 

 it once was, has fallen off considerably, the deposit being now almost exhausted. The same 

 is true to a greater or less extent for all the known diamond-fields of Brazil, and generally 

 speaking it may be said that all are now worked to only a small extent. 



Brazilian diamonds, generally considered, show certain characters which are common 

 to all diamonds, but possess other characteristics peculiar to themselves which enable an 

 expert to recognise their Braziliarr origin and sometimes even to name the actual district in 

 which they were mined. 



In size Brazilian diamonds are almost invariably small, being surpassed in this respect 

 by Indian and especially by South African stones, many of which are above the average 

 size. The average weight of Brazilian stones is ^ carat or perhaps less. Large numbers of 

 diamonds smaller in size than the head of an ordinary pin are lost in the process of washing, 

 their size not being sufficient to repay the trouble of collecting. Stones the weight of 

 which lies between ^ and ^ carat are frequent, those varying in weight from 1 to 5 or G 

 carats are rare, and the occurrence of still larger stones most unusual. In Diamantina, 

 when the yield was most abundant, only two or three stones of 16 to 20 carats were found 

 yearly, and several years might elapse before the discovery of one of still larger size. 

 Generally speaking, a lot of 10,000 Brazilian stones will contain only one stone of 20 carats, 

 while 8000 of them will weigh but one carat or less each. From 1772 to 1830, the period 



