J. P. Cooke, Jr., on Cryophyliite. Q17 
Art. XXVI.—On Cryophyllite, a new mineral species of the Mica 
Hamaly, with some associated minerals in the granite of Rockport, 
Massachusetts ; by JostaH P. Cooxg, Jr. 
IN a paper published in a recent number of this Journal* I 
described a new mineral species allied to Helvin, to which I 
gave the name of Danalite. Associated with Danalite in the 
granite ledges forming the extremity of Cape Ann, Massacho- 
setts, are two remarkable micas, one of which is the new species 
to which on account of its easy fusibility and foliated structure 
I have given the name Cryophyllite. 
_ Mineralogical Characters-—The mineralogical characters of ery- 
Ophyllite are as follows. Like other varieties of mica it crys- 
tallizes in six-sided prisms, which are frequently of considerable 
size, from one to two inches in length and of proportionate diam- 
eter. The basal cleavage is highly perfect, yielding thin flexible 
and transparent lamine, which when examined with a Peg 
microscope give a biaxial image, the angle between the optical 
axes varying from 55° to 60°. The angles 55°, 57° 30’, and 60°, 
were all measured on different specimens. The dispersion of the 
axes, if any, is so slight that its character could not with certain- 
ty be determined, the color of the mineral tending to obscure 
any such effect. The perfect uniformity of the two systems of 
rings both as to form and to color indicates that the mica belon 
more, the crystals were fre- | 
quently twinned together © .————— a 
on the plane #3, and it was observed that in such cases the planes 
| * Vol. slii, No. 124, July, 1866. ' 
