MINERALOGY OF BLACK LAKE AREA. 
23 
examined the change is not quite complete. Further changes have 
converted part of the brucite to hydromagnesite. 
Carbonates. 
ANHYDROUS CARBONATES. 
CAL CITE. 
Calcite occurs in small amounts throughout the area, forming 
veinlets and filling fissures in the various rods ; and, where it is found 
in vugs and druses, it is sometimes well crystallized. Transparent 
crystals with bright faces are, however, the exception. As a general 
rule they are white and drusy, with rounded edges, fn some cases the 
drusy coating is obviously the result of a later deposition of microscopic 
calcite crystals on the plane surfaces of the original transparent crystals, 
since the coating can occasionally be removed, leaving the faces of the 
underlying crystal sufficiently bright to admit of measurement on the 
goniometer. At other times the rounded drusy surfaces appear to have 
been produced by a partial re-solution of the crystal. 
An exhaustive study of the crystallography of the calcite was not 
attempted ; none of the crystals appeared to be very complex in forms 
and those present could, as a rule, be easily identified by inspection. 
Some of the best crystals were measured on the two-circle goniometer, 
and in doubtful cases the forms present on the drusy ones -were confirmed 
by measurement with the contact goniometer. The forms observed are 
given in the following table: 
Crystal Forms of Calcite . 
Dana 
Goldschmidt (G») 
Michel-Levy 
m 
1010 
b 
1120 
e* 
r 
1011 
P* 
1121 
P 
M 
4041 
nr 
4481 
e* 
r 
3584 
b = 
11-2-13-4 
d* d* bi 
f 
0221 
4>' 
2241 
e 1 
<f> 
0554 
V* 
5-5-10-4 
el 
The measured and calculated angles for the form T 7 (3584) are as 
follows : 
Measured 
Calculated 
<P 
P 
8° 05' 
8° 13' 
60 00 
59 55 
