14 
BULLETIN NO. 32. 
No examples of twinning have been observed amongst the material, 
that has been available for examination. The crystals do, however, show a 
persistent tendency toward parallel development which has resulted in the 
formation of peculiarly handsome groups as illustrated in Figure 7. 
Inyoite. 
Table arranged to show the combination of forms on the nineteen measured 
crystals. 
is 
£ 
01 
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n 
I 
3 
i 
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i 
13 
to 
£ 
3 
& 
3 
& 
3 
& 
13 
1 
13 
13 
1 
3 
m 
13 
1 
3 
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3 
& 
3 
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13 
8 
13 
I 
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rH 
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.-I 
C 
001 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
b 
010 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
a 
100 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
m 
110 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
z 
120 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
• + 
+ 
k 
011 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
V 
021 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
i 
101 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
h 
201 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
P 
111 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
y 
111 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
g 
312 
+ 
OPTICAL PROPERTIES. 
Several trials were made to determine the optical characters, using some 
of the larger crystals ; these, however, did not yield satisfactorily concordant 
results owing, it is presumed, to included individuals of selenite. 
It became necessary, therefore, to select a number of the smaller 
crystals whose purity was beyond question. Wulfing’s 1 method was em- 
ployed for determining the position of the optic axial angle, the intermediate 
index having previously been obtained by the total reflection method. 
* E. A. Wulfing, f. Kryst. 36, 1902, 402-407. 
H. Rosenbusch and E. A. Wulfing, Physiography, 1st part, pp. 326-327. 
