Chap. VI. ] 
MANGANESE -GAENETS. 
167 
by Penfield's method of 4 02. Again the state of oxidation was not 
determined. The two analyses are given below : — 
Spessartite. 
Spandite 
Chargaon. 
Carbham 
Specimen No. 1030. 
Specimen No. ^ 
SiOz 
3471 
35 24 
AI2O3 
805 
6-48 
Fe203 
8-38 
23-90 
MnO 
38-83 
16-3'. 
MgO 
5-40 
2 0^ 
CaO ... 
4 07 
13-20 
BaO 
Trace 
018 
Ti02 
Nil 
Moisture at 100° C. 
Nil 
Nil 
Combined water 
Undet. 
Undet. 
100-34 
99-41 
The analyses are given above as returned by the analysts. Since t^ie 
state of oxidation had not been determined, I calculated the foregoing 
analyses into terms of the general formula 3RO.R203.3Si02, assuming 
the state cf cxidation required for the constituents of the analysis to 
agree with this formula. The analysec thus re-arranged are given in 
the table on the next page. It will be seer that in the case of the Char- 
gaon garnet it was found necessary t'^ add on 0-96 °/q of oxygen 
so as convert a portion of the MnO into Mn203, whilst an excess of 
3-00 °/q of MgO above the amount of constituents required for the pro- 
toxide group has been excluded from the re-arranged analysis. In the 
case of the Garbham garnet it was foimd necessary to add 0-26 '^/^ of Si02, 
and to reject 0-27 °/o of oxygen, because a small portion of the Fe203 
had to be converted into FeO for the protoxide group. The interesting 
features of these analyses are first the presence of BaO in one case in 
traces and in the other to the extent of 0*18%, and secondly the 
existence, as deduced by calculation, of Mn203 in the R2O3 group in the 
Chargaon garnet, it being usually thought that all the manganese in 
garnets is present in the form of MnO. On pages 349 and 2-57 will be 
found analyses of gondite from Wagora in the Chhindwara district, 
Central Provinces, of opalized kodurite from Kotakarra in the Vizaga- 
patam district, Madras, and of opalized kodurite from Boirani in the 
Ganjam district, Madras ; and further, an analysis of the garnet con- 
tained in each rock deduced by calculation from each rock analysis. 
These 5 garnet analyses, all calculated to 100, are given below. Their 
composition has already been discussed in connection with the 
nomenclature of the manganese-garnets on the preceding pages. 
