Custer weekly chronicle. [volume] (Custer City, S.D.) 1890-1931, 1913-11-01
MICA.-SUPPLIES AND USES
Mica From Large Mines Average Better in
Size and Quantity than that From
Many Small Deposits.

are capable of large annual production,
and could be made to supply all but that
small part of the domestic demand
which calls for the softer Canadian
amber mica. This output could be
readily furnished if some of the mines
in several of the mica. producing states
were operated on large scale, or even
as they have been worked in the past.
These mines are in North Carolina, New
Hampshire, South Dakota. Idaho. New
Mexico, Virginia, and Colorado. Other
deposits in these states and in other
states already mentioned could be
developed to meet increasing future
demands.
The cost of production of mica in the
United States is considerably greater
than in some other countries, especially
India. 1t is probable that this differ.
ence in cost could be reduced by more
extensive operation of the larger and
better deposits by improved methods.
The mica obtained from the large mines
generally averages better in size and
quantity than that from many small
deposits. Were many large mines in
operation, there would be little need of
working small prospects,, for the large
mines would supply all the small sheet
and scrap mica demanded by the trade
along with their output of more valuable
mica.
In some years the domestic produc-
tion of sheet mica egnals or exceeds the
imports in quantity, but it is generally
less in value. This is owing to the fact
that small sheet mica can not be i'm
ported in competition with the domestic
production protected by duty of 20 per
cent ad valorem with an additional 5
cents pound for rough mica and 10
cents pound for trimmed mica Ac-
cordingly the imports consist of larger
and more valuable sheets under less
relative duty than the small mica. The
unmanufactured sheet mica imported
nto the United States is graded and
trimmed around the edges, so that there
will be minimum of waste in manu-
featuring. The quality of the best
domestic mica as to transparency, color,
cleavage, and fexibility is equal to that
OF the same variety produced in India
and other countries. Some mica of
inferior quality, however, produced
during the mining and preparation of
domestic mica, is sold as third and fourth
grade in the United States, because
material for these grades from foreign
mines is not sufficient value to pay the
import duty and be placed on the
market.
Mica has wide commercial applica-
ton. in the form both of sheet mica and
of ground mica. The most extensive
use of sheet mica is in the manufacture
of electrical apparatus, but consider
able quantity is still used for stoves, for
gas-lamp chimneys, for lamp shades,
etc. The demand for mica for glazing
is small, and only the best quality and
the larger sheets are thus used. Both
large and small sheet mica is used in
the electrical industry. "Micanite," or
build-up mica board, for the manufacture
of which small, sheet mica can be used,
is substituted for large sheet mica in
much electrical work. Mica serves as a
perfect insulator in various parts of
dynamos, motors, induction apparatus,
witchboards, lamp sockets, and nearly
every variety of electrical appliance
The domestic or muscovite mica is
satisfactory for all insulation except for
commntators of direct-current motors
and dynamos built up of bars of copper
and strips of mica. For this purpose
no mica is as satisfactory as the phlogo-
pite or Gambler mica" This mica is of
about the same hardness as the copper
of the commutator segments, and there
fore wears down evenly without causing
the machine to spark.
Statements have been made in the
literature on mica that mica which |
contains incusions of black "specks,, of
iron oxide is worthless for electrical |
insulation. That this is not the case is |
proved by the continued production of
such mica from some ofthe mines of the |
United States and its use by large and
reputable manufacturers. Tests made |
on domestic "specked" mica have shown |
a capacity to withstand currents of high |
voltage. The black "specks" of most |
domestic mica is caused by extremely |
thin magnetic dendrites between the |
laminae. These dendrites are so thin |
in some mica as to be transparent, and |
apparently do not penetrate the mica |
sheets. They do not detract greatly |
from the insulating capacity of the mica |
The i'll favor with which black 'speck- |
ed" mica has been regarded arose from |
troubles caused by certain imported |
mica in which inclusions of metallic |
minerals penetrated the laminae, there
by destroying the insulating qualities. |
A large quantity of scrap mica-small |
sheets and the waste from the manufac- |
ture of sheet mica-is ground for |
different uses, among which are the |
decoration of wall paper and the manu-
facture of lubricants, fancy paint, and |
nodded mica for electrical insulation
Ground mica applied to wall paper
gives a siyery luster. When mixed
with grease or oils finely ground mica |
and other bearings. Mixed with shellac |
or special compositions, ground mica is |
nodded into desired forms and is used |
in insulators for trolley wires. Ground |
mica for electrical insulation must be |
free from metallic minerals. Mica used |
for fabrication should be free from |
gritty matter. For wall paper and |
brocade paints ground mica with a
high luster is required, and such lusteI
is best obtained by using clean, light
colored mica and grinding IL under |