ixxviii 
MANGANESE DEPOSITS OF INDIA. 
In cases where the mineral replaced by the attacking solutions is 
spandite, the action can be represented as taking place according to 
the following equation, when we must suppose that the manganese 
derived from the garnet is added to that deposited from the solution. 
2[3(Ca,Mn)0.(Fe,Al)203.3Si02]* + 3MnH2(C03)2 + SOg + 6H^0 = 
Spandite. 
= 0 (MnOg.HoO) * 2(Fe,Al)203 4 3CaH2(C03)2+6Si02. 
The ores formed by these secondary processes can be divided into 
three groups : — 
1. Those formed by the replacement of rocks, such as quartz-felspar- 
rocks, not originally containing manganese. In this case all the 
manganese is of external origin. 
2. Those formed by the replacement of rocks, such as kodurite, that 
contain a fair amount of manganese silicate, the manganese of the latter 
being added to that of the attacking solutions. In this case the larger 
proportion of the manganese is of external origin. 
3. Those formed by the decomposition in situ of rocks composed 
almost entirely of manganese silicates, to the manganese of which a 
further portion, brought by the attacking solutions, is added. In this 
case about half of the manganese is of external origin. 
The ores formed according to these three methods arc shown below : — 
1. Pyrolusite and psilomelane. 
2. Psilomelane with some braunite. 
3. Psilomelane with braunite as specks and patches. 
Depths lo which the ores extend. 
The solution of this question seems to depend on the determination 
of the depths at which kaoliniza^^ion takes place. Of the two reagents, 
carbon dioxide and .sulphuric acid, by which the kaolinization might 
have been effected, carbon dioxide is regarded as the more probable. 
The conclusion reached is that kaolin is formed near the surface rather 
than at considerable depths ; in fact, according to Lindgren, kaolin is 
found in the zone of oxidation, giving way to sericite at greater depths. 
The formation of the manganese-ores and the kaolin must have taken 
place since the rocks of the kodurite series came into the zone of 
weathering, as defined by Van Hise. The depth to which the zone cf 
* Ca and Mn assumed present in equal molecular proportion."*. 
