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



it is associated a quartz rock with large well-formed garnets 

 but this has the aspect of vein material. 



From an unknown locality in the state of Espirito Santo a 

 specimen is also at hand showing secondary manganese oxide 

 with garnet and well crystallized graphite. The ore that is 

 being exported from Nazareth in the state of Bahia is, judg- 

 ing from a specimen received from the gentleman above men- 

 tioned, of the same type as that described from the tunnel at 

 the Morro da Mina. The polianite (?) is coarsely crystalline 

 and strongly predominant in quantity over the garnet, which is 

 in great part replaced by pseudomorphic skeletons of secondary 

 silica. This specimen contains no graphite, but I am informed 

 that a considerable proportion of the Nazareth ore is graphitic. 



The almost constant occurrence of graphite with these man- 

 ganese-bearing rocks is very suggestive of a genetic relation, as 

 is also the converse association noted by Weinschenk in the 

 graphite deposits of Bavaria and Bohemia. It is not, however, 

 uniformly distributed throughout the ore bodies, as might be 

 expected if the relation was a necessary one, and, moreover it 

 occurs also quite independent of the manganese-bearing rocks 

 as in the granite at Agua Limpa and in a decomposed schist a 

 kilometer or more distant from Sao Goncalo. In the former 

 case the graphite appears in both the granite and manganese- 

 bearing rock but in greater force and purity in the former. In 

 the latter the graphite-bearing rock has no manganese ores in 

 the immediate vicinity and the garnets with which it is abund- 

 antly charged give no trace of that metal. This schist is also 

 heavily charged with iron in the form of a fine hematite dust 

 and it may be presumed to have been originally a garnet-am- 

 phibole schist, or perhaps an eclogite. This is not the place 

 to discuss the probable origin of the graphite, but it may be 

 remarked that the hypothesis of a gaseous introduction pro- 

 pounded by Weinschenk for the Bavarian and Bohemian 

 occurrences seems to me to best meet the conditions observed 

 in this district. Whatever may be its mode of origin and 

 admitting a doubt as to a necessary connection between graphite 

 and manganese-bearing rocks, it is worthy of note that the two 

 elements carbon and manganese certainly show a predilection 

 for each other's society. 



Sao Paulo, Brazil. 



