E. 8. Dana—Mineralogical Notes: Tysonite. 481 
3. TYSONITE. 
tinct cleavage parallel to the unit prism £ ‘The observed 
planes for the species are then: 
O- (0001, c) 1 (LOI, p) 
I (iol) 2 (2021, 9) 
i-2 (1120, 4) 2-2 (1121, s) 
+ On two crystals the angle between O and 1 admitted of accu- 
rate measurement; the result was 
O.~1, 0001,1011 = 38°25’ and 38°24}! 
Of these the former is accepted as the fundamental angle, as 
the planes affording it were best suited to give accurate results. 
The length of the vertical axis is then. | 
c = 0°68681; 
and the more important angles calculated from it are: 
Calcula Measured. 
ra ee 0001..1011 = 38°25’* 38°25’ and 38°24)’ 
a2, ~2031 = 6746 67.42 
a 2-2, P12) =. 6S 6F 53 42 approx. 
7, 1010 .1011 = 51 35 
al (ov. 2-2),1010.0111 = 171 54 
iy Y ~2021 = 3214 
~ 9-8, 51 = 46 34 
i-2 ~ 2-2, 1V0 4 1190 = 6 8 
1 23; 1011, 1121 = 26 20 26 50 approx. 
be 1 (pyr). OTL 301K: ee 6 8 
141 (basal), 1011, 1011 = 103 10 
x 
