448 A. F. Rogers — Manganese Minerals. 



difficult task, but it is equally important with the deter- 

 mination of the minerals. 



The order of succession of the minerals of this manga- 

 nese deposit is as follows : tephroite, hausmannite, rho- 

 dochrosite, pyrochroite, and psilomelane. The place of 

 barite cannot be fixed definitely, but it seems to be earlier 

 than the rhodochrosite. It probably occurs in several 

 generations. 



Tephroite is undoubtedly the earliest formed mineral 

 present. It was probably abundant at one stage in the 

 history of the deposit but is now present as residual 

 specks. The alteration products of the tephroite are 

 indefinite, ill-defined substances to which no name can be 

 assigned. 



Hausmannite, although occurring in euhedral crystals, 

 was probably formed later than the tephroite, for vein- 

 like areas of hausmannite surround and extend into areas 

 of tephroite and there is no evidence of more than one 

 generation of hausmannite. 



Ehodochrosite is certainly later than the tephroite and 

 hausmannite, for it occurs in veinlets cutting these min- 

 erals. It is often associated with barite and replaces 

 the barite. 



The pyrochroite is a relatively late mineral, for it 

 occurs as a replacement of hausmannite and is common 

 in euhedral crystals along seams. It is also later than 

 a part at least of the barite. 



The pyrochroite in turn yields to a brown hydrous 

 manganese oxide which may possibly be the amorphous 

 equivalent of manganite. 



Finally the psilomelane was formed as a crust on the 

 exterior of the bowlder probably after it was detached 

 from its place of origin. 



The above order of sequence seems reasonable in view 

 of the fact that most of the minerals show a general 

 increase in the state of oxidation of the manganese from 

 the early to the late stages. In the tephroite we have the 

 manganous state (2MnO.Si0 2 ) ; in hausmannite, we have 

 an intermediate condition (Mn 3 4 ), and finally in psilo- 

 melane a still higher state of oxidation (Mn0 2 ). 



The bowlder undoubtedly represents a block detached 

 from its original location in the hills above, in some past, 

 probably remote, period. With the exception of the 

 barite it contains no gangue minerals, although lacking 



