248 ECONOMIC GEOLOGY 



the crystalline rocks. (See Fig. 123.) It passes into solution as 

 a carbonate or a sulphate to be redeposited as a carbonate, oxide, 

 or hydroxide under varying conditions and in a variety of forms. 

 The dioxide, hydrous or anhydrous is very common and is often 

 seen in dendritic infiltrations so abundant in the sericite schists 

 of Newbury, Vermont, and elsewhere. It is sometimes observed 

 as a black coating on river pebbles and on the various rocks sur- 

 rounding manganiferous mineral springs. M. Thresh cites small 

 hard black nodules closely resembling seeds in the bowlder clays 

 of Essex, England. Similar bodies have been found by W. M. 

 Doherty on the surface of the ground in Australia. 



The dioxides, pyrolusite and polianite, together with psilome- 

 lane are the most important ores in the metallurgy of manganese. 

 The two former minerals have no analogue among the compounds 

 of iron while the latter is a colloidal complex closely resembling 



^rf^f^": -.-.' vX ' ".' vTv-V ..".. ; ..' V7*?>7<r-n 

 7T. i. ,.. .?^C^- : &'vXV.''&^ 





FIG. 123. Lens-shaped masses of manganese ores interbedded with sedi- 

 mentary rocks. 



some of the sedimentary ores of iron. F. R. Mallet has observed 

 pyrolusite and psilomelane as an integral portion in some of the 

 Indian laterites. O. A. Derby regards the manganese ores of 

 Queluz, Brazil, as residual deposits derived from rocks in which 

 the manganese garnet was the most constant and characteristic 

 silicate. 



Wad, or bog manganese, is dissolved from the various rocks in 

 the same manner as bog iron and redeposited under similar con- 

 ditions. Bog manganese usually, if not always, bears varying 

 quantities of iron and bog iron quite frequently carries manganese. 



Character of the Ore Bodies. In the United States the manga- 

 nese ores occur in lenticular masses, stringers, pockets, grains and 

 nodules (Fig. 124). The Brazilian ores most nearly correspond 

 to a bedded deposit. 



H. Hies makes a four-fold division of the manganese ores as 



