X64 GEOLOGICAL RECONNOISSANCE 



The air-dried mineral lost 2.1 per cent, of moisture at 220 deg. F. 



The amount of free oxygen was ascertained by Mohr's method to be 

 7.82 per cent. Taking into consideration the quantity of free oxygen 

 contained in the manganoso-manganic oxide, we obtain for water expelled 

 at a red heat 10.653 per cent.; hence, the composition of the mineral may 

 be thus expressed: 



Protoxide of manganese 47.781 



Free oxygen 7.820 



Silica 26.230 



Alumina, with trace of iron 6.245 



Oxide of cobalt 0.104 



Baryta 1.875 



Lime trace 



Water 10.653 



100.708 



Subtracting silica and alumina, as adventitious intermixtures, and cal- 

 culating the remaining constituents for 100 parts, we obtain for the wad 

 the following composition: 



Protoxide of manganese 70.03 



Free oxygen 1 1 .46 



Oxide of cobalt 0.15 



Baryta 2.75 



Lime trace 



Water 15.61 



100.00 



No. 23. Braunite (?), from Poke bayou, Marion county. 



Massive; texture finely granular; lustre submetallic; color dark steel 

 gray; hardness 5.5; strikes fire with steel; powder grayish-black; much 

 more easily reduced to powder, than the two preceding minerals; wea- 

 thered surface shows brown spots of hydrate of peroxide of iron. 



Before the blowpipe, infusible; on charcoal in reduction flame, becomes 

 pale reddish-gray at the point of contact with the charcoal; in a matrass, 

 yields a little water; with fluxes, gives the manganese reactions. 



Dissolves in hydrochloric acid with evolution of chlorine, leaving a 

 residue of silica. 



Composition dried at 220 deg. F: 



Protoxide of manganese 75.386 



Free oxygen 7.979 



