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MA NGANESE DEPOSITS OF INDIA : MINERALOGY. [ PaeT I : 
of the above formula. One of these is when the ratio of Mn to Si is 
infinity. Tlien the formula becomes — 
MnO + Mn02 = Mn203, 
thus taking in the doubtful cases of minerals having the simple formula 
Mn203. The other alternative is when the ratio of Si to Mn is infijiity. 
The formula then becomes — 
lInO + Si02 = MnSiOs, 
which is the formula of rhodonite. 
In pursuing this variation of the formula to its logical conclusion I 
am not suggesting that there is necessarily any direct connection between 
braimite and rhodonite, especially as one is tetragonal and the other 
trichnic in crystalhzation. To establish this connection it would probably 
be necessary to prove the existence of a series of compounds of gradually 
increasing ratio of Si to Mn, corresponding, of course, to an increase in the 
ratio of MnSiOs to Mn203 in the other method of expressing the formula 
of braunite. I have considered this general formula for braunite to show 
the connection between the different varieties of this mineral, as other- 
wise it might be considered necessary to propose different names 
for minerals of different formulae. I do not, however, suppose that 
it is a true formula as regards structure. It is more probable that a 
rbange in the ratio of Si to Mn indicates a change in the number of 
molecules of MnO + Si02 relative to molecules of MnO + Mn02, and not a 
change within the molecule itself. 
The formulae of the above specimens of braimite, making due 
allowance for the more important of the replacing constituents, work 
out as follows according to the mR203 + ?;MnSi03 method : — 
Garividi . . . 15(Mn,Fe)203-4MnSi03. 
Kacharwahi . . . 7(Mii,Fe)203.2MnSi03. 
Kajlidongri . . . 3]\In203. (Mg,Ca) Si03. 
In the first two cases the alkahne earths are not present in sufficient 
quantity to be entered up in the formula. In the third analysis the iron 
is sufficiently insignificant in amount to be omitted from the formula ; 
but it so happens that the MgO and CaO are just a httle more than suffi- 
cient to replace all the R in the RSi03 group. Hence it seems that this 
is to be regarded as a rather unusual variety of braunite, exhibiting, more- 
over, a lower specific gravity than usual, namely 4"70, this being, of course, 
due to the replacement of manganese by magnesium and calcium. 
To see how the braimites of other countries fit in with the formulae 
given above I have reduced some of the published analyses of foreign 
braunites into terms of oxides of manganese and sihca, by replacing lime. 
