Chap. V. ] 
MANGANHEDENBERGITE. 
131 
the mineral is caUed manganhedenbergite and the formula can then 
be written as Ca(Fe,Mn)(Si03)2. 
T found a specimen of this mineral loose in a pit that had been excavat- 
Occurrence and charac- Crystalline limestone at Junawani in 
ters. the Xagpur district. It had evidently been 
derived from the limestone, from which it had become separated, 
apparently through the decomposition of the enclosing rock. The speci- 
men is a piece of one crystal about 2J inches long at right angles to 
the basal parting, and 2| inches by 1| inches across the longest and 
shortest measurements of this parting. The parting is well-marked and 
shows a vitreous to pearly lustre. Under the microscope it is seen to be 
the result of the formation of very thin twinning lamellae. The lustre 
on rough cleavage fractures parallel to the vertical axis is resinous- 
vitreous and the colour greenish brown. In one place where the pyroxene 
is transparent the true colour is seen to be sherry-brown There are 
often a large nimiber of small copper-coloured mica scales, intercalated 
along the well-marked prismatic cleavages so that their basal cleavage 
planes are parallel to the vertical crystallographic axis of the 
pyroxene. At one end the specimen passes into crystalline limestone 
in which there is a httle spessartite. The hardness of the pyroxene is 
between 5 and 6. 
Under the microscope the mineral shows well-marked basal partings 
and much less weU-marked prismatic cleavages in sections parallel to the 
vertical axis of the mineral. But in the basal sections the characteristic 
prismatic cross-cleavages of a pyroxene are well seen. Extinction 
angles (c a c) on the sections prepared measured up to 33i°, but it is 
not certain that any of these sections were truly parallel to the cKno- 
pinacoid. In thin sections the mineral is colourless, but when the sections 
are thicker the colour is pale brownish. The mineral often .shows various 
inclusions, particularly of mica, but sometimes of spessartite. Con- 
sequently, it was very difficult to prepare a pure sample for analysis, 
and it is probable that the sample analysed was not quite free from 
these inclusions ; but their amount cannot have been sufficient to account 
for nearlv the whole of the mai'ganese present. Hence there can be 
little doubt that the mineral really is manganhedenbergite and net heden- 
Composition bergite containing inclusions of mangpniferous 
minerals. The specimen analysed was foimd 
to have a specific gravity of 3'31. The analysis was carried out by 
I K Z 
