Chap. III.] 
BRAUNITE. 
that the three different examples of braunite correspond to the three 
following formulae : — 
Garividi 15Mn203.4MnSi03 = 19]VIn0.16Mn02.4Si02 = 19[MnO + (]\rn,Si)02] 
Kacharwahi 7Mn203.2MnSi03 = 9Mn0.7Mn02.2Si02 = 9[MnO +{Mn,Si)02] 
Kajlidongri 3Mn203.MnSi03 = 4MnO.3M11O2.SiO2 = 4[MnO + {Mn,Si)02] 
It will be seen from the above that although the formulae of these 
three specimens of braunite show three different ratios of Mn203 to 
MnSi03, yet the number of molecules of the manganese protoxide is 
equal in each case to the smn of the number of molecules of the dioxides 
Mn02 and SiO^, so that the three formulae can be re-arranged as 19, 9, and 
4 times the formula MnO -f (Mn,Si)02 ; the difference between the three 
braunites lies in the ratio of Mn to Si in the (Mn, Si) group, being 15 : 4, 
7 : 2, and 3:1, that is 3| : 1, 3| : 1 and 3 : 1 in the three cases. The formula 
MnO + (Mn,Si)02 may thus be taken as the general formula of braunites 
free from appreciable quantities of replacing constituents. It must be 
remembered, however, that in making the above calculations, portions of 
the manganese were put in the place of the oxides of iron, barium, calcium, 
and magnesium, returned in the original analysis. At first sight it might 
seem a difficulty that the iron was returned in the original analysis as Fe203, 
and that there is no sesquioxide group in the above formula for braiinite 
that the iron could replace. It must be remembered, however, that 
there is no means of telling in what condition the iron really was in the 
original mineral. To fit in with this formula it must have been in the 
ferrous condition with a corresponding proportion of the manganese 
originally returned as protoxide in the peroxide form. On this view the 
general formula that takes in aU the above varieties is — 
(Mn,Fe,Mg,Ca,Ba)0 + (Mn,Si)02. 
In most cases the amounts of baryta, Hme, and magnesia are small, 
so that, although it is necessary to take them into account in the cal- 
culations, they can be omitted from the formula. The most usual formula 
for braunite will then be — 
(Mn,Fe)0 + (Mn,Si)02. 
In the case of braunites containing only an insignificaut amount of iron 
the formula can be further simplified into — 
MnO + (Mn,Si)02. 
Since the ratio between the Mn and Si in the (Mn, Si) group is a variable 
one it is evident that there are two further possible simphfications 
