Chap. V.] 
5?CH~FPERITE AND UBBAMTE. 
135 
seems to form part of the gondite series. In Xo. 7, Jothvad, the 
vellow pyroxene occurs in a portion of the rocks of the gondite serie3 
that has been included in the granite surrounding the hill in which 
these rocks occur ; this rock is best considered as a contact rock 
formed bv the interaction between the granite and the metamorphic 
rock it has picked up. As regards the pleochroism it must be 
noticed that the axis colours have been determined on sections in thin 
slices of the containing rocks. These sections necessarily cut the 
pyroxene in various directions and it is not usually possible to determine 
exactly what this is. Consequently in testing with a quartz wedge I 
have simply recorded the colour corresponding to the direction of great- 
est and least elasticity as a and c respectively, choosing for this test 
only those sections that seemed to be cut fairly close to planea 
parallel to the vertical crystallographic axis. When this section 
happened to be clino-pinacoidal then the colours recorded would be those 
really corresponding to the a and c axes. When however the section 
happened to be parallel to the ortho-pinacoid, then of course one of the 
axis colours recorded would be b, whilst the other would be compounded 
of both the a and c axis colours. In such a case, however, the extinc- 
tion would be straight ; to avoid this confusion I have chosen in aU 
cases those sections giving the largest extinction angles and therefore 
those approximating most closely to the chno-pinacoid. The b axis 
colour must in all these cases be very similar to the colours recorded for 
the other axes, as it would otherwise be noticeable. From the figtires 
given above for schefferite and urbanite it wiU be seen that the values 
of the extinction angles for these two minerals are as follows : — 
Schefferite . . . • ^ " 7 =-1' to 4oA'. 
Urbanite . . . . a • <: =16= to 22^; 
whilst in the examples in the table the value of this angle varies from 0^ 
to 60°. Probably in most cases these Indian pyroxenes are monoclinic, 
but in the case of the Kajlidongri mineral it seems possible that it is 
orthorhombic. 
It is difficult on such insufficient data to specify any particular 
examples of the above as either scheSerite or urbanite, but perhaps 
the Sitapathur specimen may be regarded as urbanite on account of its 
reaction for sodium. 
