DIAMOND: OCCURRENCE IN BRAZIL 165 



numbers, aggregating in weight up to 1700 and 2000 carats, being found in a single small 

 nest, while few, if any, in a considerable area of the surrounding " gurgulho." 



Under the diamond-bearing " gurgulho," and resting immediately upon the solid rock, 

 there is usually a layer of clay, in which also a few diamonds are to be found. Above the 

 "gurgulho," just as in the valley deposits, is a layer of red clay of varying thickness, 

 from which diamonds are absent. When this layer is absent, as it sometimes is, the 

 " gurgulho " forms the actual surface of the ground and is covered by vegetation. It is 

 said that the observation of diamonds attached to the roots of plants, scratched up to 

 the surface by fowls, or picked up by children at play, has led to the discovery of rich 

 deposits. 



Plateau deposits at other places, such as, for example, Sao Joao da Chapada, on 

 the plateau of Diamantina and about twenty miles west of this town, differ very widely 

 from those just considered. The mines here are situated on the watershed between the 

 Rio Jequetinhonha and the Rio das Velhas, and on the prolongation of the straight line 

 which connects the important deposits of Boa Vista, on the hills near Curralinho (Fig. 35) 

 with those of La Sopa. These deposits were discovered in 1833. Extensive workings were 

 carried on for a long period, but were finally discontinued owing to the exhaustion of the 

 deposit. In spite of this the place remains extremely important from the scientific point 

 of view, for here may be gathered data which afford material help in solving the problem 

 as to the nature of the original mother-rock of diamond in this region. 



The diamond occurs here in variously coloured clays, which lie in a trench 40 metres 

 deep, 60 to 80 metres wide, and 500 metres long, somewhat resembling a deep railway 

 cutting. These clays are distinctly bedded, being inclined 50° to the east, and regularly 

 and conformably interbedded with them are beds of itacolumite inclined at the same angle. 

 All the strata, the clays as well as the itacolumite, are penetrated by numerous small veins 

 filled for the greater part with quartz (rock-crystal), rutile, and haematite. 



The yield of diamonds from these clays was very variable, but on the whole the deposit 

 was considered poor. Tschudi, who visited the place in 1860, reported that in his presence 

 forty-four carats were obtained in two hours, while on another occasion only ten small 

 stones were found in twelve tons of material. The associated minerals are the same as 

 elsewhere, the three just mentioned being specially abundant. It is a noteworthy fact, that 

 where the associated minerals occurred in abundance there diamonds were plentiful, but 

 where, on the other hand, the minerals were present to only a sparing extent, diamonds 

 also were hard to find. 



The minerals associated with the diamond are present at this locality in less proportion 

 than in the ordinary " cascalho " or " gurgulho," and the same is true also of the diamond 

 itself. As has already been mentioned, the minerals which occur most frequently are 

 quartz, haematite, and rutile, other oxides of iron and of titanium, tourmaline, &c. All are 

 found, like the diamond itself, in perfectly sharp crystals. Even the softest of the minerals 

 found here have preserved intact the sharpness and angularity of their edges and corners. 

 None show any indication of having been transported by running water. 



These circumstances have led those who have personally investigated the deposit, 

 namely, Orville A. Derby and Gorceix, to the conclusion that here, in these beds, the 

 diamond is seen in its original home, and that here, in the quartz-veins by which the rocks 

 are penetrated, it slowly took on the shape and form in which we now know it. Although 

 no diamond has ever been found actually in a quartz- vein, yet the minerals associated with 

 it occur in such situations with great frequency, and their constant association with the 

 diamond, not only here but at all other localities of Minas Geraes, seems to point to a 



