7 
no symmetrical relationship with the axial plane and hence that the mineral 
can be safely assigned to the triclinic system. Using a special compass 
designed by Fedoroff the cleavage angles were determined to be as follows: 
Co A Ci = 88° 40' 
Ci A C» = 108° 00' or 72° 
Ci A Ci => 111° 00' or 69° 
Ci A Ci = 131° 00' or 49° 
Likewise the angles between the normal to the axial plane and the normals 
to cleavages were found to be: 
0 A Cl = 150°; (S A Ci = 66°; |8 A C> = 44°. 
These last figures fully locate the position of the axial plane with respect 
to the cleavages. Again, from the plat it may be seen that, owing to their 
large polar distances, the y and 0 axes could not, respectively, be brought 
into parallel position with the microscope tube by tilting the stage. It was 
possible, however, to do so in the case of the a axis and, therefore, to calcu- 
late the birefringence (y—j3), The actual amount of retardation Ri of one 
of the rays transmitted by the crystal plate behind the other was measured 
with a babinet compensator, whereas the thickness of the mineral section 
was determined by Nikitin's method using a micrometer ocular. The 
value (y—0) =0*015, thus obtained, is exactly what w r as determined by 
calculation from the indices of refraction. 
As shown in the chemical discussion farther on, collinsite belongs to 
the Roselite group. This being so, and because of the correspondence of 
the measured angles in the two minerals as tabulated below, it follows that 
the cleavages in collinsite correspond in all probability to the faces indicated 
in the same table. 
Roselite 
Mm = 48° 47' 
CM = 89° 20' 
bm = 66° 09' 
bM = 65° 03' 
C (001) 
b (010) 
m (110) 
M (1101 
Collinsite 
CiC* 49° 
CoCi 88° 40' 
CsC* 69° 00' 
C*Ci72°00' 
Co 
C, 
c* 
Ci 
Chemical Properties 
Material suitable for analysis was carefully prepared by the writer, 
and through the courtesy of the Chemical Division of the Mines Branch 
the analytical work was carried on in duplicate by Mr. E. A. Thompson, 
with the following results: 
