6 
By oil immersion on crushed fragments the indices of refraction were 
found to be as follows : 
a « 1-632 ± 0-003; /S = 1-642 ± 0-003;t = 1-657 ± 0-003. 
The birefringence is positive and as calculated from the above figure is : 
(7 - a) = 0-025; Q S-a) = 0-010; ( 7 -/ 8 ) -0-015. 
f 
Figure 2, Collinsite from lake Francois, B.C. Optica! and crystallographic elements plotted on 
the stereographic plat of Fedoroff. (Co, Ci, C2, and C3 are cleavages.) 
The elongation was also determined to be positive. 
The results of an extensive study using the Universal stage are pre- 
sented in Figure 2, constructed with a Fedoroff stereographic plat as a basis. 
Examination of the figure (Co is the best cleavage) shows that 7 being 
the acute bisectrix, the mineral is positive; it shows also that 2V = 80° and 
that four cleavages, numbered Co, Ci, C2, C3 in order of perfection, have 
