0. C. Farringion — Studies of Brazilian Favas. 355 



Art. XXYII. — Studies of Brazilian Favas ; by Oliver C. 



Farrington. 



Among the exhibits of the Brazilian Commission in the 

 Mines Building at the Louisiana Purchase Exposition was one 

 of minerals which are found accompanying the diamond in the 

 state of Minas Geraes, Brazil. All the minerals were in the 

 form of rolled pebbles and included in addition to readily 

 recognizable specimens of tourmaline, rutil.e and cyanite, a 

 number of less easily identified species known under the gen- 

 eral name of favas. This term, derived from the Portuguese 

 word for beans, is, as is well known, a common appellation 

 among the diamond miners for minerals resembling a bean in 

 shape and size. The entire series of minerals and favas was, 

 through the kindness of the Brazilian Commission, presented, 

 at the close of the Exposition, to the Field Museum of Natural 

 History. Among the series one group of pebbles was labelled 

 goyazite, and on account of the rarity of this mineral, special 

 examination of these pebbles was made by the writer. They 

 seemed sufficiently uniform in appearance to belong to a single 

 species, since in color, shape and texture they appeared similar. 

 There were several score of the pebbles included in the lot, 

 their color being brownish yellow, their longest diameters 

 ranging from 3 to 10 mm. and their diaphaneity being none. 

 On closer investigation the pebbles were found to be less uni- 

 form than appeared at first sight, the first lack of uniformity 

 noted being one of specific gravity. Some favas were found 

 to have a specific gravity of about 3 and others of about 4. A 

 difference in the luster of the surface was also found to accom- 

 pany the difference in specific gravity, the smoother, more 

 lustrous pebbles or favas being found to be lighter in specific 

 weight than the duller ones. Qualitative chemical examina- 

 tion of the heavier, dull favas showed that they were Ti0 2 

 favas such as were first noted by Gorceix,* and later described 

 by Hussak.f They consisted of Ti0 2 with a little water. 

 They were infusible but turned dark on heating. Heated in 

 the closed tube they also turned dark and gave off a a little neu- 

 tral water. Determinations of specific gravity gave results 

 ranging from 3*97 to 4*08. A quantitative determination of 

 water gave0'6 per cent. While this form of hydrous oxide of 

 titanium probably cannot be regarded as a distinct species, it 

 seems to the writer that it is a sufficiently definite occurrence 

 to make a varietal name for it desirable. The quantity of 



*Bull. Soc. Min., vii, 179, 1884. 

 fTsch. Min. Petr. Mitth., xviii, p. 335. 



Am. Jour. Sci.— Fourth Series, Vol. XLI, No. 244. — April, 1916. 

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