Chap. III.] 
POLIANITE, 
77 
By converting the lime and magnesia into eqiiivalent amounts of 
manganese protoxide, and the ferric oxide into its equivalent of MnsOs, 
the figures given in column No. 1 below are obtained. In column No. 2 
these figures are given reduced to 100. 
MnO 
51 -69 50 -87 
MnOo 40 -"^S 
SiOs^ _8;52 _8-38 
101-62 100-00 ; 
Manganese 66-20 6.5 16 
Available oxygen " "62 7 -oO 
On comparing the figures given in column 2 with those for the three 
varieties of bravmite given on page 70, it will be seen that as regards 
the silica percentage, 8-38, the Sitapar,braunite lies about half-way 
between the formulae in which the ratios of Mnfi.^ to MnSiO, are 7:2 
and 4:1, respectively, the actual ratio corresponding to this silica per- 
centage being 15 : 4, as in the Garividi specimen. The amounts of 
MnO, Mn02, and available oxygen are, however, considerably diiferent 
from what they should be if the braunite has this formula. This 
difference can be easily explained on the supposition either that there 
is an error of 0-78 per cent, in the oxygen determination, or that all 
the protoxides do not form a portion of the braunite, and so should 
not all have been converted into manganese protoxide in the foregoing 
calculations. The formula of this braunite on the supposition of an error 
in the oxygen determination would be 15Mn203.4MnSi03 ; whilst on 
the supposition that a portion of the protoxides of lime and magnesia 
does not form a portion of the braimite, the formula would be 4M.r\^0^. 
MnSiOg. 
Polianite. 
Polianite is a mineral crystallizing in the tetragonal system in forms 
isomorphous with tin-stone. It has a composition represented by the 
formula Mn02, is too hard to be scratched by a penknife (H. — 6-6"5) 
and has a specific gravity of 4"8.3-5'03. Its colour is light steel-grey to 
iron-grey, with a black streak. This is one of the rarest of the oxide 
minerals of manganese and is found at Flatten in Bohemia. It has not 
yet been for certain identified amongst the Indian ores. 
Some specimens of manganese-ores were recently sent to the 
Geological Survey Office from the Bikonhalli deposit (known 
as Norton's Block), Shimoga district, Mysore, by Mr. Claude Fawcitt, 
chemist to the New Mysore Manganese Company. Amongst them is 
one, the characters of which suggested polianite. In general colour 
