372 
DESCRIPTIVE MINERALOGY. 
observed at this locality, with the direction 
of the cleavage. Figs. 393 and 394 repre¬ 
sent compound crystals with five and six 
sides, two of them forming a reentering 
angle. All these crystals are usually very 
perfect, and have their sides smooth and 
polished. 
This mica has been analyzed by Prof. Yon Kobeli of Munich, 
results : # 
The following are the 
Silica,. 40.00 
Alumina,._. 16.16 
Oxide of iron,. 7.50 
Magnesia,. 21.54 
Potassa,. 10.83 
Oxide of titanium,. 0.20 
Fluoric acid,. 0.53 
Water,. 3.00 
According to Dr. Horton, the mica from this locality has long been used as a substitute for 
coloured glass, for spectacles. Almost any shade of colour can be obtained by using a larger 
or smaller number of plates. 
Near West-Point, mica is of frequent occurrence in granite. It is sometimes black; at 
others, bronze-coloured. Occasionally it is met with in six-sided prisms. 
Fig. 395. Six miles southeast of the village of Warwick, in the town of the 
same name, black crystallized mica is found in a vein of feldspar in 
granite. It occurs in crystals and plates, which are sometimes a foot 
in diameter. Fig. 395 represents one of the forms observed. M on l 
150° ; M on k 120°. 
Brown mica is found in white limestone near Edenville, while the silvery variety occurs 
near the village of Amity. 
A mile northwest of Edenville it occurs in white limestone, in perfect hexagonal prisms 
with the angles 120°, and in rhombic prisms. 
In the same vicinity, there are specimens of a silvery white colour, resembling mica, but 
rather more brittle than is usual with that mineral. It melts before the blowpipe into a white 
enamel, and agrees with the characters of Lithion-mica, as given by Dr. Turner. It seems 
to pass into talc. 
Putnam County. Black mica, in rhomboidal and six-sided crystals, is found at Coldspring. 
Brewster's Edinburgh Journal of Science. IX. 175. 
