302 
MANGANESE DEPOSITS OF INDIA ; GEOLOGY. [PaRT II : 
crystallized out as diopside, epidote, garnet, microcline, plagioclase, and 
sphene, etc. If the sediment contained a fair quantity of manganese, 
either as oxide or perhaps as carbonate, then the other impurities, 
instead of forming diopside, epidote, and ordinary 
Formation of pied- gamet, gave rise to the corresponding manganiferous 
uiontite, spessartite ^ . \ . ■. • ^-^ j t 
and rhodonite. mmerals rhodonite, piedmontite, and spessartite, oi 
which piedmontite was by far the most frequently 
formed. The rhodonite and spessartite have not been analysed ; but one 
would expect them to be more calcareous than the varieties found in the 
manganese-ore bodies previously considered, namely those that were 
formed by the metamorphism of the manganese-oxide sediments asso- 
ciated with non-calcareous sands and clays. There is no need to give 
equations for their formation as they would be very similar to those 
given on pages for the formation of non-calcareous spessartite and 
rhodonite. The formation of the piedmontite may be expressed by 
the following equation : — 
2Mn203 + 2Fe203 + 5[2H20. Al203.2Si02] + 12CaC03 + 8Si02 = 
Clay (kaolin) Calcite Quartz 
■ =6[Ca2(A1.0H)(Al,Mn,Fe)2(Si04)3] + I2CO2 + 7H2O 
Piedmontite 
in which the Al, Mn, and Fe, are for the sake of simplicity assumed to be 
present in the group (Al, Mn, Fe) in equal molecular proportions. In 
cases where the segregations were mixed throughout with various im- 
purities, the whole segregation was sometimes converted into pied- 
montite, often with the admixture of a little calcite or quartz or other 
impurity, the residue of the sediment mixed up with the manganese 
oxides. On the other hand, when the nodules, bands, or beds, of manga- 
."^odu^es of man ^^^^ oxide were deposited free or comparatively free 
ganese-ore and pied- from admixture with calcareous or other material, 
iiioutite. they were compacted on metamorphism into nodu- 
les, bands, or beds, of crystalline manganese-ore. As might be expected, 
many of the nodules, which is the commonest form that the segregations 
take, are of complex composition and composed partly of manganese-ore 
and partly of piedmontite. This may be due to the original segregations 
having been composed of manganese oxides in some parts free from, 
and in other parts containing, admixed impurities. On metamorphism 
the impure portions were converted into piedmontite and the pure por- 
tions into manganese-ore. In the specimen illustrated on Plate 14 one 
nodule is composed of manganese-ore inside with a peripheral zone 
varying from to inch thick of piedmontite. This peripheral zone 
