Chap. V. ] 
MANGANESE-AMPHIBOLES. 
145 
tity of rhodonite, but to the large proportion of it that is too much 
blackened to be of use ; for it must be mentioned that a small proportion 
of oxy-alteration, as long as it does not give rise to decayed spots, 
improves; if an}i;hing, the beauty of the rock, on account of the 
mottUngs, spots, and moss-like markings it produces. A considerable 
proportion of small pieces of rock suitable for the manufacture of small 
ornaments could be obtained, but it would be very difficult to obtain 
larger pieces suitable for such purposes as the manufacture of table tops. 
Manganese-ampMboles. 
Although, in the Archaean manganese-silicate-rocks of India, the 
commonest cf the dark sihcates are garnets, with pyroxenes next, 
yet amphiboles have been found at several locaUties, in no case, however, 
except at Kajhdongri, in any but very small quantities, forming no 
appreciable proportion of the whole mass of rock in which they occur. 
These amphiboles can be divided into two main divisions according to 
their colour. One division is blue, lilac, or lavender, in colour and will 
be considered under the heading of tvinchite, a name given to the variety 
found at Kajlidongri. These have been definitely determined to be 
manganiferous. The amphiboles of the other group vary from yellow 
to greyish-green, greyish, and chocolate, although the latter colour is 
probably the result of alteration. These varieties have not yet been 
carefully investigated, but on account of their association are 
probably manganiferous and will be considered under the heading of 
dannemorite, the described amphibole to which they bear the closest 
resemblance. As regards occurrence, it is to be noticed that no 
amphiboles have yet been observed in the igneous manganiferous rocks 
of the kodurite series of the Yizagapatam and Ganjam districts, and 
that all the knoAvn occurrences of amphiboles in Indian manganiferous 
rocks are in the varieties that I look upon as metamorphic in origin, 
belonging always to the gondite series. They have been found in all of 
the three areas in which rocks of this series have been recognized, namely, 
Narukot, Jhabua, and the Central Provinces. 
Before considering the various occurrences of these amphiboles in 
_ . India it wiU be well first to give a short account 
foreign mangani- <• i • , i i -t i • 
ferous amphiboles. 01 what IS known about the mangamierous amphi- 
boles of other parts of the world. There are two 
main divisions of the manganiferous amphiboles, corresponding to the 
two following minerals : — 
Dannemorite . . . {Fe,Mn,Mg) SiOs, 
Richterite . . . [(K,Na)2, Mg,Ca,Mn] SiOs. 
I L 
