i0l6 
MANGANESE DEPOSITS OF INDIA : DESCRIPTIVE. [ PaRT IV : 
not have been sufficient, considering the amount of rock that is Hkely to 
have been drawn upon, to provide all the manganese now concentrated 
in the deposits at the surface, it would not be unreasonable to suppose 
that the average amount of manganese in the Dharwilrs of Sandur, and 
for the matter of that in other Dharwar areas of India, was considerably 
higher than 0'08 per cent. 
The principal minerals in the manganese -ore deposits of the Sandur 
Hills are psilomelane and wad, with subordinate 
preseut."'^"^*"^^ ° mi.iorals ^mounts of pyrolusite, of altered raanganite 
(' pseudo-manganite ' ), and of a hard grey crys- 
talline mineral. The typical ore is an irregular mixture of psilomelane 
Psilomelane and wad wad, in which both minerals often contain 
formed by replacement of minute Scattered Octahedral crystals of a very 
phyllite . . .. .. , , .,. 
magnetic mineral that is in all probability 
magnetite. It might possibly be mangan-magnetite ; but this it is 
not possible to test, because it would be impossible to be quite sure 
that any grains of it when isolated were free from attached or included 
manganese-ore. These magnetite grains are identical in shape and 
size with those to be found in all the phyllites and slates of these 
hills. Further the ores often contain fragments of altered rock of 
slaty aspect, usually with a reddish streak; these, which also contain 
the tiny magnetite octahedra, must be regarded as altered phyllite or 
slate^ often impregnated with or partly replaced by iron oxide. An 
examination of specimens containing such fragments shows that this 
altered phyUite or slate passes gradually into wad, the streak changing 
from reddish through chestnut to blackish brown, probably as the per- 
centage of manganese increases The wad retains both the slaty struc- 
ture and the magnetite grains of the phyllitic rock. Further, in the speci- 
mens in which it is mixed with psilomelane, it looks as if the wad finally 
passes into psilomelane, probably by the accession of more manganese. 
The psilomelane itself, although it does not show the slaty structure of 
the wad and altered phyllite, yet often does show a roughly laminated 
structure, parallel to the bedding of the phyllites and wad. From this it 
seeniS inevitably to follow that the psilomelane is the final product in the 
passage of phyllite into manganese-ore by the process of metasomatic 
replacement : the first stage of the alteration is a soft slaty rock usually 
of ferruginous character, the iron itself being probably a secondary 
