250 
MINERALOGY: W- LINDGREN 
Proc. N. A. S. 
dicular to the poorly developed orthopinacoid, extinctions of 0°are rarely- 
seen. Exact optical measurements are difficult on account of the deep 
color. Obscure hyperbolae show on the prism faces and it is probable 
that the plane of the optic axes lies parallel to the perfect cleavage (010). 
The absorption is very strong. The a ray is visible with dark yellowish 
brown color through the prism faces and the orthopinacoid and has ac- 
cording to a determination kindly made by Professor C. H. Warren a 
coefficient of refraction of 1.74; while the /3 and y rays are somewhat 
higher but cannot be measured exactly on account of the strong absorp- 
tion. The j8 and y rays therefore lie in the 010 plane of perfect cleavage 
and their absorption is so strong that such cleavage pieces only become 
translucent in extremely thin plates, with dark reddish brown color, /3 
and 7 differing slightly in depth of tint. The double refraction is strong. 
The material was analysed by Professor L. F. Hamilton of the Massa- 
chusetts Institute of Technology, who reported the following composition : 
V 2 O s 52.61 
V 2 0 4 33.34 
CaO 9.89 
MgO .27 
A! 2 0 3 Fe 2 0 3 1.89 
Silica 1 . 66 
Assuming the alumina, iron oxide, magnesium and silica to be 
impurities from the admixed shale the analysis may be recalculated to: 
V 2 0 5 54.90 
V 2 0 4 34.78 
CaO 10.32 
100.00 
From this we calculate 
54.90 
V 2 0 5 -j^ = 0.302 
v >°< - 0209 
CaO = 0.184 
56 
V 2 0 5 : V 2 0 4 : CaO = 302 : 209 : 184 
or approximately 3:2:2. The formula would therefore be 
2 Ca0.3V 2 0 5 .2V20 4 
The calculated composition of this would be: 
V 2 0 5 55.16 
V 2 0 4 33 . 54 
CaO 11.30 
100.00 
