332 J. C. BRAN^'EK OUTLINES OF THE GEOLOGY OF BRAZIL 



Zirconia. — The oxide of zirconia, which has been exported from Brazil 

 in considerable quantities within a few years past, is derived by decom- 

 position from nepheline syenites and other kindred rocks. The material 

 was first found as water- worn pebbles in stream beds and as angular 

 fragments scattered over the ground in the vicinity of the nepheline 

 rocks from which they were derived. These rocks are found in the 

 vicinity of Caldas, in the State of Minas Geraes, and near Franca and 

 Jacupiranga, in the State of Sao Paulo. It is probable that this mineral 

 may occur in other places in Brazil where there are nepheline syenites. 

 They are known at present at Cabo Frio, Campo Grande, Itatiaia, and 

 the peak of Tingua, State of Eio de Janeiro, and they probably occur at 

 many other places in Brazil. (See Derby on the nepheline rocks of 

 Brazil, and E. Hussak and J. Eeitinger on zirconia, Groth's Zeitschrift 

 fiir Krystallographie, 1903, volume 37, pages 550-579.) 



Fliospliates. — The island of Fernando de Noronha, off the northeast 

 coast of Brazil, is the only place that is known to produce phosphate 

 rock. It is found there as a Recent or Quaternary deposit, on the small 

 island known as Ilha Eapta. A few cargoes are said to have been 

 shipped, but the lack of landing facilities is said to ha^^ prevented the 

 establishment of an export business. 



Papers have been published on the subject by Bovet, Derby, Lasne, 

 Sena, and Sobragy. 



Diamonds. — Diamonds have been mined in Minas Geraes, Matto 

 Grosso, Bahia, and Parana. The diamond-mining industry of Brazil 

 declined greatly after the discovery of diamonds in South Africa, but it 

 is still conducted on a small scale. Most of the diamonds I'ound in 

 Brazil have been taken from existing stream channels, or from old 

 stream deposits where they have been concentrated by natural processes 

 from the rocks of the surrounding region. Specimens have occasionally 

 been found imbedded in the hard rocks, usually in gravels cemented by 

 iron and evidently not in place, but they have also been found in Paleo- 

 zoic quartzites. ]\Iuch has been written upon the origin of the Brazilian 

 diamonds, but, whatever their remote origin may have been, they have 

 thus far been found in paying quantities in Brazil only in stream chan- 

 nels or other deposits formed by concentration. In Parana they appear 

 to be derived from a Devonian basal conglomerate. In Bahia they come 

 from pink quartzites tentatively referred to the Carboniferous. At 

 Grao Mogol, in northern Minas, they also occur in quartzites. The min- 

 erals associated with diamonds in Brazil suggest that their genetic rela- 

 tions are with deep-seated granites, metamorphics, and pegmatites rather 

 than with eruptives. In the State of Bahia, at least, no eruptive rocks 



