130 
MANAGNE3E DEPOSITS OF INDIA : MINERALOGY. 
[ Part I : 
The latter was pleochroic in very pale pink and green, corresponding 
to a and c respBctively. The extinction angle a a t varies from 
14^ to 47^. In plaeej the green tint look^ distinctly bluish, and, 
in fact, when the tints are so pale, it is often very difficult to 
determine whether thi ^ axis colour is blue or green. With the 
quartz polarizing in gray and white of the first ordsr, the pyroxene 
polarizes in orange and red of the first order and purple of the 
second. 
Comparing the properties of the various varieties of pyroxene 
noticed in the preceding paragraphs it seems that the type of pleo- 
chroism is approximately the same in all, namely : — 
a = pink , 
h - lilac, 
c = blue, 
the depth of these various tints varying very much in the pyroxenes of 
different localities. The above scheme, which is that of the typical 
mineral of Kacharwahi, is subject to slight variations in the pyroxenes 
of other localities. Thus the lilac colour corresponding to the b axis 
may have a tinge of brown in it. causing this colour to approximate to 
the characteristic colour of titaniferous augite, whilst the blue colour of 
the c axis may have a greenish tinge in it, or may even be quite green, 
the latter phenomenon being noticed both in the igneous variety of 
.lothvad and in the variety, also igneous in origin, found at Ramdongri. 
The cause of <"he differences in the depths of the colours of the varieties 
from different localities may be due to differences in the amounts of 
manganese present, as also may be the differences in the values of the 
angle -a ^ c. But these poi nts can only be settled by the isolation and 
chemical analysis of the different varieties ; until this is done it is 
not possible to say if we are dealing with only one variety of pyroxene 
of slightly varying composition, or whether more than one mineral has 
been included under the name blanfordite. If the latter be the case 
and later it be found necessary to give a separate name to some of the 
varieties, then the name blanfordite will be reserved for the variety for 
which it was first proposed, namely that of Kacharwahi. 
Manganhedenbergit e- 
Hcdenbergite is a calcium-iron pyroxene of the formula CaFe(Si03)2. 
When a certain proportion of the iron is replaced by manganese 
