MINERALOGY OF BLACK LAKE AREA. 
65 
These were determined by measurement, mainly with the contact 
goniometer, of selected crystals which were first oriented by means of 
interference figures. 
The crystals h ave a specific gravity of 2 • 60 — 2 • 65 . Optically they are 
invariably biaxial, positive, with dispersion p < v. The acute bisectrix 
is slightly inclined to the normal to c(001), and the axial angle is variable, 
some crystals being nearly uniaxial. Most of the crystals, even when 
apparently simple, are seen to be multiple twins, on the Mica law 
(twin plane J_c in the zone cnio) , the planes of the optic axes in the 
several individuals composing the twin being inclined to one another at 
about 60 degrees. The mean refractive index is about 1*58, and the 
birefringence of medium strength, near that of quartz. 
No complete analysis of the material has been made. It is here 
designated clinochlore (as against penninite) on the strength of the 
various criteria referred to above, viz. the tabular crystal habit, the 
relatively high birefringence with its invariable positive sign, the distinctly 
biaxial character, and the very common twinning on the Mica law as 
observed under the microscope. 
Most of the specimens examined came from the Montreal chrome 
pit where the clinochlore occurs associated with vesuvianite, andradite, and 
diopside, as referred to under those species. The clinochlore, so far 
as observed, is later than the diopside and vesuvianite, but older than 
the andradite, calcite, and aragonite. Another mode of occurrence at 
the same locality shows the clinochlore as extremely thin, colourless, 
transparent, scale-like crystals of roughly hexagonal or rounded outline, 
associated with similar material of matted appearance; this variety has 
a rather small optic axial angle. It occurs filling fissures in a dark, 
brownish -black, chromite-bearing serpentine, and is at times stained 
emerald -green through reaction with the chromite; there is also a little 
associated calcite. 
At the Southwark pit, clinochlore occurs as minute hexagonal 
plates associated with colourless grossularite and reddish-brown vesuv- 
ianite. 
Clinochlore of deep greenish-blue colour, similar to that of the 
Montreal chrome pit, but not so welt crystallized, was also noted at the 
Union pit, where it occurs with bottle-green vesuvianite, brown diopside, 
and garnet. 
Kotschubeite. A rose-red chromiferous mineral, possessing the general 
characters of this variety of clinochlore, has been met with at the Montreal 
chrome pit, where it forms very small veinlets in the massive chromite 
and in places occupies fissures in dark brownish-black serpentine. It 
exhibits a very distinct biaxial figure, is optically positive, and has a 
comparatively high birefringence. 
