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MANGANESE DEPOSITS OF INDIA : GEOLOGY. [PaRT II : 
that they also produced the decomposition of the spandite-rock. Had 
this decomposition taken place without the deposition of manganese 
brought in solution by the incoming waters, the results of the action 
would probably have been the same as have already been described as 
taking place when kodurite is attacked by these solutions, namely, the 
solution of the manganese and calcium as bicarbonates, leaving behind 
little else but the ferric oxide and any alumina in the garnet as kaolin. 
In the second place the rocks in this part of the mine show every stage of 
alteration from the comparatively fresh spandite-rock to good manganese- 
ore without any signs of the porous rock that woiild be formed if the 
decomposition of the garnet-rock took place separately from the intro- 
duction of manganese oxide from elsewhere. For these two reasons 
it is necessary to suppose that the solutions that effected the decompo- 
sition of the spandite-rock also deposited the manganese oxide brought in 
from outside. The solutions to produce this combined decomposition 
and deposition would be the alkahne carbonate solutions saturated with 
manganese bicarbonates. The reaction can be supposed to take place 
somewhat on the lines of the following equation : — 
2[3{Ca,Mn)0.(re,Al)203. 3Si02]* + 3MnH2(C03)2 + 3O2 + CH2O 
Spaiidite. 
= C(Ma02.H20) + 2(Fe,Al)203 + 3CaH2{C03)2 + 6Si02. 
It will be seen that I have introduced oxygen into the above equation. 
Altercation took place course known whether the manganese 
under oxidizing condi- was Originally deposited in the protoxide condition 
and subsequently oxidized, or whether it was 
originally deposited in the more highly oxidized condition. In whichever 
condition it was deposited the oxide was probably hydrated, and in so 
far as it is now free from water has since become dehydrated. I think, 
however, that it was probably originally deposited in the higher state of 
oxidation ; in the first place because I think the formation is still going 
on to a certain extent, as for example at Kodur, obviously suflficiently 
near the surface to be within the range of oxidizing influences ; and in 
the second case because there seems to be no sign of any mineral, such 
as manganosite (MnO), pyrochroite (MnO.H20), or rhodochrosite (MnC03), 
in the lower state of oxidation, although these might have been formed 
and since entirely raised to the higher state of oxidation due to 
subsequent prolonged subjection to the influence of waters containing 
* Ca and Mn asauined to bo piesoiit in C(ju!il inolocular proportions. 
