Chap. V. ] 
WINCHITE. 
151 
the main winchite-bearing band. In this rock the mineral is found in 
small tufts tending to be radiate in structure. 
From the fine-grained quartzite mentioned above I have been able 
to obtain several small crystals sufficiently well 
Crystallographic formed to permit of the measurement of the angle 
coaracters. n, • i • 
mm . In general these crystals are simple prisms, 
showing no other faces, and with irregular terminations. But in one case 
an embedded crystal was found showing, in addition to the prism, the 
clino-pinacoid 6, a small steep clino-dorae, and the basal plane, c, sloping 
sUghtly forwards. The portion of the crystal \-isible is only TS mm. 
long, and about 1 mm. from acute angle to acute angle of the prism. 
For the determination of the angle mm'" , I was able to separate three 
suitable crystals. These can be designated I, II, III. 
I. This is Jr mm. long and TS mm. wide and is dark blue in 
colour. It is a simple prism sUghtly tapering. AU the fac&s 
are rather dull owing to the projection of included specks of 
braunite. One face is cracked at one end and another has a 
little white crust on a portion of it. Using only the acute- 
angled edges of the crystal several measurements made over 
each of these edges gave a mean value of 55° \T for the 
prism angle mm'". 
II. This is the best crystal and is an unusually transparent one of 
lavender-blue colour. It is 2' 5 mm. long andO'OSmm. broad. 
It is a simple prism, with the faces finely striated in a 
vertical direction, and with a few included specks of braunite. 
The reflections from all the faces except one were good. 
Measurements taken aU the way round, using all the faces 
gave 55^ '21V as the mean of several determinations. Lying 
on one of its faces on a glass sUde on the stage of the 
microscope the mineral shows well the characteristic 
pleochroism of winchite, namely from rich lilac, or even 
violet, to sky-blue. The axis corresponding to the lilac colour 
is the one nearest to the vertical crystallographic axis, so 
that the crystal is one of what has been designated the basic 
variety. The crystal is irregularly terminated at both 
ends. 
III. This is a portion of a large crystal, and is 0-6 cm. long and 
i-5 mm. broad. It is opaque darkish cobalt-blue in colour 
