504 Hidden and Washington—Contributions to Mineralogy. 
The following figures give a good idea of its habit, though 
in the perspective figure the prisms are elongated. 
2 3. 
As fundamental angle the following was finally decided upon, 
it being the mean of about a dozen good determinations. 
x - v, (1011 ~ 1122) = 18° 52’ giving a: ¢ == 1: 0°734335. Kokscharof gives: 
2 a@:c=1:0°734603. 
The following list of angles may be here inserted : 
Caleulated. Observed. 
cna, 0001. 1011 = 40° 18” 40° 154’ 
car, 0001, 1012 = 22° 584! 22° 584’ 
cay, 0001 , 2021 = 59° 281” 59° 31’ 
caz, 0001 , 303] = 68° 321’ 68° 36’ 
GAY, 1120, 1122 = 53° 424! 53° 414 
@a-8, 1120. 1121 = 34° 14” 34° 134 
rar, 1012 .0112/'==22° 31” D22E3 2% 
y 8, 2021 , 1121 = 25° 31” 95° 354 
yo, 2021 .3142 = 12° 454! 12° 15” (approx.) 
i z (8031), v (2131), 7 (2132), 0 (8142) and 
h (2130) were small and gave rather poor | 
images, but the other planes were well 
polished and gave good results. 
What is probably a cruciform twin 
of apatite, from this locality, was also 
examined. It was composed of two sleu- 
der, pale bluish green crystals. The fig- 
ure shows the only occurring planes. 
One crystal was slightly displaced from 
the other, but the prisms of both were 
perfectly parallel. ‘The following meas- 
urements were made, giving as a twin- 
ning plane s (1121, 2-2). The first two measurements are 
the most reliable : 
a . 0, = 68° 28’, giving twinning plane ~a@ = 34° 14’ 
ENTS. <= Bei C= BP 2a 
mY 0m, — 92°15’, “ “ .@= 383° 32’ 
