COMMON MICA. 81 
These stones, when properly cut and smoothed, are 
of indispensable utility to carpenters, cutlers, and others, 
for sharpening their cutting instruments upon. Those 
of the finest grain are used for lancets, penknives, and 
razors. For this purpose their surface, wi*en used, is 
covered with a small quantity of oil ; by which, after 
a while, they are rendered considerably harder than 
they were at first. They ought to be kept in damp and 
cool places ; for, if much exposed to the sun, they be- 
come too hard and dry for many purposes to which they 
are applied. 
There is a vulgar and erroneous notion that hones 
are holly wood, which by lying in petrifying water, 
have 'been thereby converted into stone. The greater 
number of them have a fine and a coarse side. From 
the circumstance of their having been originally brought 
into this country from Turkey and the Levant, they are 
sometimes called Turkey stones. They are now found 
in Saxony and Bohemia, in North Wales, and near 
Drogheda, in Ireland. 
The powder of whet slate is sometimes used, instead 
of emery, for the cutting and polishing of metals. 
MICA FAMILY. 
123. COMMON MICA, GLIMMER, or MU8COPY 
GLAS'8, is a mineral substance of foliated texture, which i$ 
capable of being divided into extremely thin leaves that have 
a sensible elasticity, and are transparent. 
The colour of mica is greenish, sometimes nearly black, red- 
dish, brown, yellow, or silvery white, with, occasionally, a me- 
tallic lustre on the surface. Mica is so soft as easily to be 
scratched; and, when divided across the plates, seems rather 
to tear than break. 
This is one of the most abundant mineral substances 
that is known. It not only occurs in a massive and 
crystallized state, but it enters into the composition of 
many rocks ; is found filling up their fissures, or crys- 
