218 J, P, Cooke, Jr., on Cryophyllite. 
of cleavage of the two crystals were absolutely coincident, prov- 
ing that the rhombic prisms are rectangular and not oblique, as 
De Senarmont has previously shown to be true of other crystals 
of the mica family. 
The color of cryophyllite in axial directions is dull emerald 
green, not unlike glass colored with protoxyd of iron, and so 
deep that the laminz are opaque unless quite thin, but like other 
colored micas it is dichrous and appears brownish-red in the di- 
rection of the lateral axes. The color of the streak is light gray 
with a tint of green. The luster is brilliant on the cleavage face 
inclining to resinous. The hardness is from 2 to 2°5 and the 
specific gravity 2°909. 
Before the blowpipe cryophyllite very easily fuses with some 
intumescence to a greyish enamel bead, and it even fuses in flakes 
of considerable size in the flame of a candle, so that its fusibility 
is from 1:5 to 2 of von Kobell’s scale. It imparts to the flame 
of a Bunsen’s lamp a most brilliant lithia reaction, and by ex- 
amining the colored flame with a spectroscope the presence of 
potassium, sodium and rubidium may also be readily discovered. 
The amount of sodium however must be exceedingly small as it 
does not sensibly modify the lithia flame as seen by the naked 
eye, and the same is true to astill greater degree of rubidium. 
The presence of rubidium is best recognized by mixing the pul- 
verized mineral with pure pulverized sulphate of lime, exposing 
asmall bead of this mixture supported by a loop of fine plati- 
num wire to the flame of a gas blowpipe and examining the 
flame with a spectroscope. The characteristic double blue line 
of rubidium is then seen very distinctly for a few moments, but 
soon disappears. No trace of cxsium could be discovered, either 
by the mode of experimenting just described or by examining 
the platinum salt obtained in the course of the analysis, by the 
partial precipitation of the alkalies with chlorid of platinum. 
Heated alone in a closed glass tube cryophyllite alighian 
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was made with three portions of the same powder. From 
