246 ECONOMIC GEOLOGY 



product has no commercial significance save in its alloys. Its 

 specific gravity is 8, melting point, 1245 C, and its atomic 

 weight is 54.93. 



Ores of Manganese. Manganese never occurs native on 

 account of its remarkable affinity for oxygen. The element is 

 widely distributed in nature in somewhat limited quantity. 

 The oxides and the hydrous oxides are far the most important 

 minerals. 



Alabandite, MnS, 63.1 per cent. Mn. The only sulphide of the 

 metals with an olive green streak. 



Pyrolusite, MnO 2 , 63.2 per cent. Mn. In pulverulent form 

 known as the black oxide of manganese. 



Polianite, Mn0 2 , 63.2 per cent. Mn. Distinguished from pyro- 

 lusite by its superior hardness and tetragonal crystallization. 



Manganosite, MnO, 74.4 per cent. Mn. 



Pyrochroite, Mn(OH) 2 . The corresponding iron compounds are 

 unknown in nature. 



Manganite, Mn 2 3 , H 2 O, 62.4 per cent. Mn. 



Braunite, 3Mn 2 3 , MnSi0 3 , 69.68 per cent. Mn. 



Hausmannite, Mn 3 4 , 72 per cent. Mn. The iron equivalent is 

 magnetite. 



Psilomelane, H 4 Mn0 5 , 45 to 60 per cent. Mn. With barium 

 and potassium variable. 



Wad. The formula and percentage of manganese varies 

 widely. 



Rhodochrosite, MnCO 3 , 61.7 per cent. MnO. 



Rhodonite, MnSi0 3 , 54.1 per cent. MnO. 



The last two minerals are pink or rose colored and capable of 

 some industrial application for decorative interior work. 



Origin of the Ores. Alabandite occurs in Colorado in asso- 

 ciation with the carbonate of manganese and the sulphide of 

 silver, lead and iron. The action of alkaline sulphides upon the 

 soluble salts of manganese in alkaline solution will effect its pre- 

 cipitation. The mineral is too rare to be of great commercial 

 significance. It is used to a small extent in the metallurgy of the 

 metal. 



The numerous oxides and the hydrous oxides of manganese are 

 all of secondary origin. Forschammer and Dieulafait report 

 manganese in solution in oceanic waters. According to E. Mau- 

 mene 1 it occurs in the ashes oifucus serratus. According to F. W. 

 Clarke manganese as an oxide or hydroxide exists in all deep-sea 



