260 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. [ PaRT 11 
In the case of the Boirani rock there are five minerals to be considered 
instead of three, namely apatite, orthoclase, albite, garnet, and opal. 
In this case, as no specific gra\aty determination of the garnet of this area 
is available, it is necessary to assume a figure for the opal and calcidate 
the specific gravity of the garnet. Taking the specific gravity of the 
opal to be 1 • 90, of apatite 3-20, of albite 2 '62, of orthoclase 2-57, and of 
the rock analysed 2 • 65, the value of this constant for the garnet is found 
to be 3' 76, a considerably lower figure than for the Vizagapatam garnets, 
but one which is probably about correct. It is then ne<^essary to reconvert 
the opal into the felspar that it has in all probability replaced. The 
original felspar, judging from the character of that still left, was probably 
orthoclase containing a small proportion of soda in the form of micro- 
perthitic inclusions. Assuming, for the sake of ease of calculation, that 
the original felspar was pure orthoclase, then the original composition 
of the rock works out as follows : — 
Apatite 2-87 
Orthoclase 63 '07 
Albite 3 05 
Garnet (grandite) 39 '87 
Ti02 0 27 
CiiO .......... trace 
109 13 
Bringing both these analyses to 100 they may be re-stated as foUows : — 
Kotakarra Boirani 
kodurite. kodurite. 
Apatite .... 3 '361 . . . .2*62 
Orthoclase ... 41 '29 .... 57 "80 
Albite . . . . ... . . . . 2"79 
Garnet , . . . 55 "04 . . , .36-55 
Ti02 . . . . 0'29 . . . . 0 24 
CuO .... 0'02 .... trace 
100 "00 100 -00 
Specific gravity of original rock . 3-23 .... 2 92 
1 The apMtitc is lower in this analysis, than it would have boon on a large sample 
of the rock ; for the apatite is arranged in bands in the rock, and the apatite bauds were 
scarce in the specimen analysed. 
