ALUMINA. 
371 
Fig. 388. 
Fi s- 387 - Fig. 387. The angles of the crystal are 
about 119°. 
Near the banks of Muscolunge lake, in 
the town of Alexandria, this mineral is found 
in small but regular and perfect six-sided 
tables of a dark brown colour, in white lime¬ 
stone. Fig. 388. M or M / on k 120°. 
The plumose variety of mica has also 
been found associated with spinelle in white limestone, near the village of Oxbow. 
New-York County. The dolomite at Kingsbridge, and elsewhere, contains mica, which 
is sometimes in the form of perfect six-sided tables. It exhibits a variety of colours. The 
plates are seldom of large size. 
Orange County. Mica of almost every variety of colour and form occurs in this county. 
Many of the localities are of great interest. One of these perhaps most deserving of notice, 
is on the bank of a stream running from Mount Basha pond, near Forshee’s iron mine, in the 
town of Monroe. The mica is in augite rock, or rather in a bed of this mineral, with scattering 
crystals of quartz contained in gneiss. The plates interlace each other in various directions, 
and some of them are of large size. Dr. Horton and myself obtained a specimen, now in the 
State Cabinet, which is twenty-two inches in diameter; but plates of nearly three feet in 
diameter have been observed at the locality. They are, however, usually fractured by the 
agency of water and frost, so as to prevent their removal in an entire form. The colour of 
this mica is greenish, and it breaks into rhomboidal fragments.* 
At the Wilks or Clove mine, in the vicinity of the preceding, plates of mica of a blackish 
green colour, and from one to five inches in length, are found associated with the magnetic 
iron ore. 
Near Greenwood furnace, mica occurs in black or greenish black crystals, which are some¬ 
times six or seven inches in diameter. It is associated with 
crystallized pyroxene, coccolite and calcareous spar. The 
_ . ^ most common form is an oblique rhombic prism. Fig. 389, 
a on a' usually about 120° ; P on a 114° to 115°. 
There is also a regular six-sided prism, the sides inclining to each other at an angle of 120° ; 
but in these, as in the preceding, the inclination of the terminal to the lateral planes is about 
114° or 115°, and 65° or 66°. Figs. 390, 391 and 392 represent sections of various forms 
Fig. 390. 
Fig. 391. 
Fig. 392. 
/f° 
i 60 y 
/20* j J20\ 
/Jao ° 
\ T 
\ / 
P | 
/t20° 
P 
/go 
120 C ‘/ 
/GO 
eo\ 
* The mica at this locality seems to be sufficiently abundant for profitable exploration. 
