CHEMICAL RELATION OF IRON AND MANGANESE. 367 



proportion, thus giving rise to the common low -manganese iron 

 ores. 



The hydrous oxides of iron and manganese, however, are not 

 isomorphous,^ and, therefore, when they are precipitated together, 

 as in bog- deposits, the association is often much less intimate 

 than in the cases just mentioned, and is simply due to the fact 

 that, under certain conditions, the oxides of both metals are pre- 

 cipitated in the same place. 



CAUSES OF THE SEPARATION OF IRON AND MANGANESE. 



When iron and manganese ores occur in more or less separate 

 deposits, it becomes necessary to suppose the action of influences 

 different from those which cause the deposition of both together, 

 and such influences are to be found in the different modes of pre- 

 cipitation, under certain conditions, of the two metals. It has 

 been shown by Fresenius^ that certain warm springs, on reaching 

 the surface, first deposit hydrous sesquioxide of iron, and farther 

 on carbonate of manganese. This not only points to the well- 

 known fact that carbonate of iron is more easily oxidized than 

 carbonate of manganese, but it also leads to the belief that the 

 bicarbonate or other salt of iron in the water is more easily oxid- 

 ized than the manganese salt. 



An action somewhat similar to that described by Fresenius 

 readily explains the occurrence of manganese sometimes in 

 entirely separate deposits, sometimes in distinct but closely alter- 

 nating deposits. 3 Under certain conditions, if the waters from 

 which the precipitation took place were moving, the iron and 

 manganese, owing to the difference in oxidability, as stated above, 

 would be laid down in different places, resulting in the formation 

 of deposits of iron ore free from manganese, and manganese ore 

 free from iron in different positions along the plane of the same 

 geologic horizon. Such occurrences are often seen in the iron 



' The hydrous oxides of iron are not crystalline. - See p. 363. 



3Bischof suggests that the action described by Fresenius causes the separate 

 deposition of iron and manganese ; and also that it explains the occurrence of large 

 deposits of manganese ore in regions where the iron ore contains least of that ingredi- 

 ent. (See Elements of Chemistry and Phys. Geol., Vol. III., pp. 531-532.) 



