MINERALOGY OF BLACK LAKE AREA. 
35 
These crystals measure 
up to 3 mm. in length and 
about 1 mm. across the 
prism. They occur in 
fissures and druses in the 
white massive diopside, 
notably in the immediate 
neighbourhood of the con- 
tact between the latter and 
serpentine. The commonly 
associated minerals are 
vesuvianite and andradite, 
both of pale yellow colour, 
and generally some thin 
blades of aragonite; the 
andradite in particular was 
noted as invariably occur- 
ring with the diopside of 
this habit. 
Less frequently, col- 
ourless crystals were obser- 
ved, somewhat similar in 
habit to that just described, 
but with the faces in the 
prism zone developed to 
about the same extent as 
those of the acute hemi- 
pyramid ; Figures 7 and 
8 illustrate this type. 
Like the last, these crystals 
are associated with the 
white massive diopside; 
but, it was noted that the 
druses in which they occur 
are almost always adjacent 
to veinlets or grains of chromite and that, in addition to the diopside, 
they usually contain crystals of emerald -green vesuvianite; other minerals 
which may be present are pale green andradite, caleite, and occasionally 
clinochlore. The diopside crystals measure up to 4 mm. in length and 1 
mm. across the prism, but as a general rule they are rather smaller than this. 
Figure 9 shows an intermediate habit, idealized to represent the 
average of a number of measured crystals, but with the length of the 
prism somewhat exaggerated. 
Figure 13. Diopside, colourless crystal from the 
Montreal chrome pit; contact twin, with o(100) 
as twin-plane, parallel to which the crystal is 
flattened. 
