2'.K) MANGANESE DEPOSITS OF INDIA : MINERALOGY. [ PaRT I : 
microscopic research on these latter rocks may lead to the discovery of 
ottrelite in them also. Accepting the definition according to which 
the mineral always contains manganese it is evident that the 
sediments from which the phyllite or schist was formed must have con- 
tained this element in appreciable proportion. 
The localities at which I have found ottrelite are (1) in mica-schists 
at the boundary of the villages of Sitasaongi and Chikhla in the Bhandara 
district, at the point mentioned on page 763, (2) in the phyllites and phylli- 
tic schists lying on the west of the Balaghat-ore body, and (3) in the 
mica-schists overlying the manganese-ore body at Ukua, in the Bala- 
ghat district. It is not all the micaceous phyllites and schists at these 
localities, however, that contain ottrelite, and it is often very difficult to 
detect any external difference between two rocks one of which contains 
ottrelite, whilst the other does not. The characteristic rock found both 
at Sitasaongi and Balaghat contains quartz, muscovite, tourmahne, 
rutile, and a black ore, probably ilmenite, in addition to the ottrelite. 
The curious intergrowth of the rutile and ilmenite is noticed on page 313. 
When visible in the hand-specimen the ottrelite is seen to be of a darkish 
green colour. The evidence on which I base the determination of this 
mineral as ottrelite is (1) the fact that it gives a distinct reaction for 
manganese when it is possible to isolate a piece for testing, and (2) its 
appearance under the microscope. In the first place in sections showing 
the basal cleavages the extinctions are often oblique, the value of this 
angle rising to as much as 18°. In the second place the birefringence 
is very low, whilst thirdly the pleochroism is that characteristic of 
ottreUte. The pleochroism schemes made out from slides of the 
Sitasaongi and the Balaghat rocks, respectively, are shown below : — 
Sitasaongi. Balaghat. 
a = olive-green, it = olive-green, 
b — plum-blue to indigo-blue. b = indigo-blue, 
c = pale yellowish green. c = pale yellowish. 
The scheme given for Sitasaongi is exactly that given in Rosenbusch- 
Iddings, 4th edition, p. 292. Occasionally twinning is seen in sections 
across the cleavage. 
