64 
MUSEUM BULLETIN NO. 27. 
lining narrow fissures in an aplitic rock, and has the form of slender 
prismatic crystals arranged in divergent groups; they attain a size of 
1 cm. in length by about 3 mm. in width, but are commonly narrower 
than this, and they have a silky lustre. Examined under the microscope 
the crystals are found to be biaxial, negative, with weak double refraction, 
and the extinction angle, Bx a A c-axis, was measured as 17 degrees. 
MICA. 
The minerals of the mica group are not at all common in the area, 
either as constituents of the principal rocks or otherwise. Biotite is 
occasionally present in some abundance in the granite, but in general 
this rock is essentially hornblendic and contains no biotite. A brown 
coloured mica is associated with the colerainite at the old Standard 
mine, and specimens of a tourmaline-bearing pegmatite from the dump 
at the same mine carry crystal flakes of muscovite (damourite). 
CLINOCHLORE. 
Clinochlore is fairly widespread, and sometimes occurs in very 
sharply defined crystals, as for example at the Montreal chrome pit. 
These crystals are tabular in habit, quite transparent, and have a deep 
bluish-green colour by transmitted light, the tint being paler in the thinner 
crystals; when extremely thin they are colourless. More commonly the 
mineral forms irregular cleavable masses, with colour varying from green 
to white, and these at times display a massive or compact structure. 
The best crystals collected have a width of 1 cm. or less and are 
not more than 2 mm. in thickness, though poorer and opaque crystals 
of larger size occur. In form they are six-sided plates with bevelled 
edges; the base has the usual pearly to vitreous lustre, is usually faintly 
striated parallel to its edges, and is seldom sufficiently flat to yield a 
single-image reflection. The faces of the other forms are also found on 
examination to be, for the most part, very imperfect; occasionally a 
crystal will display between the two basal planes one or more faces which 
are perfectly sharp and have a high and somewhat greasy lustre, but it 
generally happens that these planes are heavily striated, have a dull 
lustre, and yield continuous strings of images when examined on the reflect- 
ing goniometer. Some crystals exhibit as many as six of such imperfect 
planes lying in a zone; but owing to their character and also to the fact 
that most of the crystals are found, both by the presence of reentrant 
angles and by optical tests, to be repeatedly twinned, it has not been 
possible to determine these forms with accuracy. The following forms 
seem to be well established, however, as occurring on crystals from the 
Montreal chrome pit. 
G (001) u (227) fi (112) 
(101) d (225) » (132) 
t (205) 
f (401) 
u 
d 
m. (112) 
n (225) 
0 (0-11-24) 
3 (059) 
t (043) 
