352 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. 
[Part II : 
a svirplus of 3 per cent, of magnesia. The state of oxidation of the 
manganese and iron was not determined, because the quantity of fairly 
pure garnet separated for analysis was not sufficient for this purpose. 
Owing, however, to the small quantity of the sesquioxides, AI2O3 and 
Fe203, it is necessary to assume that a portion of the manganese is 
present in the form of manganese sesquioxide, Mn203, in order to form 
the group R2O3 in the garnet formula. This is, of course, somewhat 
imusual ; for manganese is not usually supposed to be present in the 
sesquioxide portion of garnets, but only in the protoxide portion. The 
variation in the amount of manganese present in these two garnets is 
considerable, but the general composition of them is sufficiently 
near to the standard composition to warrant the use of the term spes- 
sartite to designate them. The variation in the amount of manganese 
present could well account for the variation in the colour of the 
manganese-garnets of the Central Provinces. In this case it is somewhat 
difficult to compare the colours of the two garnets , because the Wagora 
garnet was distributed as small granules in a piece of gondite where its 
colour was to some extent masked and d luted by the quartz with which 
it was associated. Nevertheless, I should say that the Wagora garnet 
was, as would be expected from the smaller percentage of manganese it 
contains, distinctly paler in colour than the Chargaon garnet. In the 
latter case the specimen analysed was obtained by breaking up and care- 
fully picking two or three trapezohedral crystals, which were of a deep 
orange colour. 
The only other member of the gondite series whose composition 
^ we need consider is that composed of rhodonite 
rbSonfte-qmirtz-rock. ^iid quartz. Here again it is obvious that the 
rock may show every variation in composition 
between that of quartz -rock free from rhodonite and that of 
rhodonite-rock free from quartz. The Indian rhodonites have not yet 
been examined analytically, so that it is not known if they conform to 
the composition of the typical mineral, i.e. have the composition 
expressed by the formula MnSi03, or if a portion of the manganese is 
replaced by some other element such as calcium. Assuming the 
Central Provinces rhodonite to have the theoretical compostition, then 
the composition of rhodonite-rock would be as follows : — 
MnO 54-04 
SiOj 45-96 
corresponding to a manganese contents of 41-86. Assuming the specific 
gravity of rhodonite to be 3-63, the chemical composition of rhodonite- 
