214 0. A. Derby — Manganese Ore Deposits of Brazil. 



effervescence with a very abundant separation of gelatinous 

 silica, leaving an insoluble residue of graphite and a heavy 

 whitish sand, consisting almost exclusively of spessartite with 

 a slight admixture of minute black granules. The solution 

 shows a. large amount of manganese with a comparatively 

 small proportion of lime and magnesia. 



The specimen of the quartzite-like type obtained from the 

 bottom of the mine, or rather quarry, also gives a certain 

 amount of effervescence and separation of gelatinous silica and 

 thus differs from the almost pure spessartite rock previously 

 reported, in which, however, the former existence of other 

 elements was deduced from the existence of secondary quartz 

 and asbestiform amphibole. In places this type shows a con- 

 siderable admixture of rose-colored rhodonite concentrated in 

 streaks and patches so as to present the appearance of an acci- 

 dental rather than an essential element of the rock. Rhodo- 

 nite without the characteristic rose color was also found in one 

 specimen as a predominant element, with a slight admixture of 

 spessartite, but without the readily soluble carbonate and sili- 

 cate element. 



Specimens of the dark-colored rock selected with reference 

 to a presumed higher and lower percentage of the carbonate 

 element were submitted to Dr. Eugene Hussak, who has kindly 

 communicated a preliminary note on their chemical and min- 

 eral composition in advance of a paper on the rocks and min- 

 erals of the manganese deposits that he has in preparation. 

 The results of a partial analysis are given below under I and 

 II, to which are added, under III, those given in the above- 

 cited paper for the type composed almost exclusively of spes- 

 sartite. 



I II III 



CO, 22-62 4-59 



SiO s ._ 11-80 27-67 38\47 



MnO 47-52 57-48 27'90 



A1.0, ) 75Q 141 21-07 



Fe„0 3 j ' ° U 2-48 7-38 



Cat) 3-76 1-82 4-70 



MgO 6-27 4-60 



Strong traces of titanium, cobalt and zinc were found in 

 Nos. 1. and II, which also carry a very perceptible amount of 

 graphite, of which minute traces were also found in No. III. 



Dr. Hussak reports that the microscopic examination shows 

 the rocks to be composed of a carbonate (rhodochrosite ?), an 

 olivine-like silicate (tephroite) and spessartite, the latter being 

 in small amount and extremely minute grains in No. II and in 

 greater amount and larger grains in No. I. Some sections 



