284 Cross and Hillebrand—Cryolite from Colorado. 
cube and octahedron, and particles detached from the same are 
isotropic in action in polarized light. Supposing that this sub- 
stance must be ralstonite in exceptional development, enough 
material for the following partial chemical analysis was selec- 
ted, being carefully freed from attached particles of pachnolite 
and other anisotropic minerals, by microscopical examination. 
The Al, Ca and Mg were accurately determined, the Ka and 
Na, owing to an unfortunate mishap, only approximately. No 
water could be detected by direct test upon a small portion. 
Fluorine was present in quantity, and the percentage given 
below is calculated on the assumption that the metals are fully 
combined with i 
Al 11°40 
Ca 0°72 
(aS eWay eae aR omey wees oe, mer 0°22 
Ka 28°94 
Na 99 
F .-46°98 
= —— 
98°16 
we are inclined to believe that the two minerals are not 1den- 
tical. 
GEARKSUTITE. 
mong the minerals from St. Peter's Dome, gearksutite is 
quite abundant. It is not formed from other minerals by 
quartz it is specially developed. oe 
"In appearance, it corresponds closely to the description of the 
Greenland mineral, as given by Dana, the resemblance to the 
* Dana, System of Mineralogy, 5th Ed., p.130. + Groth, . c., pp. 460 and 481- 
