173 



SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



hydro-phosphates, yttrium phosphates (sometimes containing titanic acid), diaspore, rutile, 

 brookite, anatase, ilmenite, magnetite, cassiterite, red felspar, cinnabar, and gold. Garnet, 

 and staurolite have also been observed here and recently euclase, but the last only as a rarity. 

 Of these minerals, cassiterite, felspar, and cinnabar have never been found in Minas Geraes 

 in association with diamond. Schrauf argued from the occurrence of these minerals, and 

 especially from the association together of tourmaline, garnet, zircon, staurolite, rutile, &c., 

 that the rocks, from which have been derived the diamond-sands of the Serra da Chapada, 

 were allied to the gneisses and syenites of southern Norway. It has been stated in 

 descriptions of the geological structure of these mountains that they are built up of these 

 particular rocks, but neither in this nor in other diamond districts in Bahia has any thorough 

 geological investigation been made, and since the minerals associated with diamond are the 



Serra da Chapada 







Fig. 36. Occurrence of diamond in the Serra da Cincord, Bahia. 



same in Bahia and in Minas Geraes, it is probable that the occurrence is also the same, 

 namely, in itacolumite. 



Especially rich finds were made in the year 1844 in the Serra da Cincora (SincorA). 

 This range is situated in longitude about 41° W. of Greenwich, and extends from south-west 

 to north-east between latitudes 13° 15' and 12° 15' S. It forms the south-eastern spur of the 

 Serra da Chapada (Fig. 36), with which it is connected at its southern end ; it separates the 

 basin of the Rio de Sao Francisco from that of the Rio Paraguassu, and constitutes 

 the collecting-ground of these rivers. This range, the Serra da Cincora, and that of the 

 Serra da Grao Mogol in Minas Geraes, closely resemble each other, both are rugged and 

 inhospitable, and it is highly probable that the Serra da Cincord. consists of itacolumite, 

 although the neighbouring heights are built up of granite and gneiss. 



The discovery of diamonds here was due to the observation of a slave, a native of the 

 diamond district of Minas Geraes, who, while engaged in minding cattle, was so struck with 

 the similarity of the soil to that of his home that he began searching for diamonds, and 

 before long collected 700 carats. Scarcely had this find become known, when eager searchers 



