228 J.P. Cooke, Jr., on Cryophyllite, 
clase variety. Very fine green colored crystals of the last have 
en obtained here, and good erystals of the usual color are 
abundant. Associated with the orthoclase I have frequently 
noticed a compact variety of albite distinguished by a peculiar 
luster and very marked striation on the plane of easy cleavage. 
It resembles somewhat, in outward aspect, oligoclase, but the 
mineral had the characteristic cleavages of a clinoclase feldspar, 
and the angle O on 72 measured with an application goniometer 
93°. Moreover it contains, if any, only the merest trace of lime. 
The albite is actually imbedded in the orthoclase, and the inti- 
mate association of these two heteromorphous species is worthy 
of notice. 
Malacone.—The same vein contains also a peculiar variety of 
zircon, which is probably identical with the malacone of Scheerer, 
only somewhat more altered. The crys- 2, 
tals have the general form represented 
in the figure, and resemble the crystals, 
of zircon from Expailly in France. On 
account of the great predominance of the 
one lvand 71, they resemble the rhom- 
ic dodecahedron of the regular system, 
and can only be distinguished from this 
form by the distribution of the modify- 
ing planes; since on account of the 
strong curvature of the faces the limits 
of necessary uncertainty in the measure- } 
ment of the angles cover the whole difference between this 
form and the corresponding form of zircon. In the ordinary 
method of representing the crystals of zircon the relation of 
the forms just referred to does not appear; but if we refer the 
planes of the zircon crystals to axes corresponding in position 
to those of the allied form of the regular system, the really close 
affinity of the two becomes evident. Thus the ratio of the axes, 
which in the regular system is unity, is in zircon a: b=0-906: 1, 
and the angle }: on 71, which in the dodecahedron equals 120°, 
is in the zircon crystal equal to 123° 19’. In the figure here 
given the crystal has been drawn and the planes lettered with 
reference to the axes of the dodecahedron, and this must be 
borne in mind when comparing it with other figures of zircon. 
The most striking peculiarity of the crystals is the strong curv- 
ature of the terminal faces, which has been indicated in the fig- 
ure, and which, as already intimated, renders accurate measure- 
ments impossible. Nevertheless, within the limits of necessary 
uncertainty the angles measured the same as those of zircon. 
The small planes not lettered on the crystal for want of space 
are w and 23. 
The color both of the crystal and the powder is brownish-red, 
