424 E. C. HARDER AND R. T. CHAMBERLIN 



hoe keep the mass constantly stirred up, so that it has a general 

 consistency and appearance not unlike thin mortar (Fig. 25). The 

 running water carries away the clay and materials of lesser specific 

 gravity, while the coarse portions of the gravel, and the minerals 

 of higher specific gravity such as the diamond, fragments of hema- 

 tite, etc., remain behind. Later, after screening out the coarser 

 pebbles, the diamonds are picked out of the final concentrate on the 

 hatea, or washing sieve, by hand. 



The diamonds of the Diamantina district generally show dodeca- 

 hedral crystallization with rounded faces. Many of those in the 

 chapada deposits have rough faces and a dark grayish-green coat- 

 ing, but the majority have smooth or striated faces. Some of the 

 stones in the present river gravels show surface corrasion. 



The majority of the diamonds mined in the district vary in 

 size from J carat to 4 or 5 carats, though occasionally stones are 

 found weighing up to 10 carats. The largest diamonds ever found 

 in the Diamantina district, according to Dr. Derby,^ weighed less 

 than 100 carats, and very few have been found weighing over 50 

 carats. The largest of the Brazilian diamonds — the "Star of the 

 South," the "Star of Minas," and the "Dresden" diamonds — have 

 all come from the Bagagem district in southwestern Minas Geraes. 



In brilliancy the Diamantina diamonds exceed the South African 

 diamonds, and there is a smaller percentage of "off-colored" stones 

 found. Beautiful bluish-white stones are abundant, and stones of 

 other colors such as lemon-yellow, cognac-brown, rose, green, and 

 blue are occasionally found. 



We are indebted to Professor T. C. Chamberlin, Professor C. K. 

 Leith, and Professor Eliot Blackwelder for criticisms and sug- 

 gestions, and to Dr. O. A. Derby for much information. 



' O. A. Derby, "A Notable Brazilian Diamond," Am. Jour. Set., XXXII (191 1), 

 191. 



