Phap. v. ] 
BLANFORDITK. 
129 
gonal and hexagonal cross-section with the angles of a pyroxene. These 
prisms vary in length from i up to nearly J inch, ar>r\ are dark brown 
with a reddish tinge. Under the microscope they exhibit the following 
pleochroism -cheme : — 
a— .rose, 
b=pa!e v;oif>t-Lin\vri to lilac. 
c=groenish blue to pale blue. 
In one case the n axis colour seemed to be green without any tinge ok 
blue, so that, the other axis colour visible being pink, the mineral might 
be mistaken at first sight for hypersthene. That it cannot be this, how- 
ever, is shown by the fact that the extinction is not straight, being 32^ 
in the section that shows the green colour best. Moreover, the c axis 
colour in hypersthene corresponds with the vertical crystallographic 
axis f, whilst in this mineral vertical sections often show the axis 
approximating to parallelism with the vertical crystallographic axis 
The angle a « c varies from 0' to 53^ and the angle c c from 37° to 
G8°. The index of refraction is high and the birefringence consider- 
able, the polarization colours being sometimes as high as green of the 
second order, in sections in which the felspars polarize in greys. The 
specific gravity of the mineral is somewhat higher than that of the typi- 
cal blanfordite of Kacharwahi. being determined as 3"264 and 3'268 on 
two separate specimens by means of Klein's heavy Uquid. The value 
of this constant can, therefore, be taken as 3"26 to 3'27 for the pyroxene 
from this rock. The mineral gives a distinct, but not very strong, re- 
action for manganese. 
The metamorphic rock in which p}Toxene exhibiting the blanfordite 
type of pleochroism occurs is a banded one, of which some layers hiAe 
the outward aspect of a biotitic sandstone of rather fine grain, whilst 
others suggest a very fine-grained quartzite. Under the microscope the 
' biotitic sandstone ' is seen to be composed of quartz, microcline, 
apatite, black manganese-ore. an orange-coloured mica, and a pyroxene. 
The last occurs in ragged plates often intergrown with mica, whilst 
some plates form a sort of network enclosing in its meshes rounded 
prisms of apatite with some quartz. The pleochroism shows that a 
is pink and c blue, whilst the one extinction angle measured was 
c A c= 19° A section of the bands resembling quartzite consisted 
essentially of a mosaic of quartz with a fair abundance of pyroxene. 
I ^ 
