posits are
likely to be small. For these reasons mining operations cannot be
organized on a large scale, but are ordinarily hand-to-mouth operations
near the surface. A large amount of hand labor is involved, and the
Indian deposits are favored by the cheapness of native labor. The output
of a district is from many small mines rather than from any single large
one.

Pegmatites which have been subjected to dynamic metamorphism are often
not available as a source of mica, because of the distortion of the mica
sheets.

The mining of a mica is facilitated by weathering, which softens the
associated feldspar, making it an easier task to take out the mica
blocks. On the other hand, iron staining by surface solutions during
weathering may make the mica unfit for electrical and certain other
uses.

Scrap or ground mica is obtained as a by-product of sheet mica and from
deposits where the crystals are not so well developed. Black mica
(biotite) and chlorite minerals, which are soft and flexible but not
elastic and are found extensively developed in certain schists, have
been used to a limited extent for the same purposes.

MONAZITE (THORIUM AND CERIUM ORES)

ECONOMIC FEATURES

The mineral monazite is the source of the thorium and cerium compounds
which, glowing intensely when heated, form the light-giving material of
incandescent gas mantles. Welsbach mantles consist of about 99 per cent
thorium oxide and 1 per cent cerium oxide. Cerium metal, alloyed with
iron and other metals, forms the spark-producing alloys used in various
forms of gas lighters and for lighting cigars, cigarettes, etc.
Mesothorium, a by-product of the manufacture of thorium nitrate for gas
mantles, is used as a substitute for radium in luminous paints and for
therapeutic purposes. The alloy ferrocerium is used to a small extent in
iron and steel.

The world's supply of monazite is obtained mainly from Brazilian and
Indian properties. Before the war German commercial interests controlled
most of the production, as well as the manufacture of the thorium
products. During the war German control was broken up.

The United States has a supply of domestic monazite of lower grade than
the imports, but is dependent under normal conditions on supplies from
Brazil and India. The American deposits are chiefly in North and South
Carolina, and have been worked only during periods of abnormally high
prices or of restriction of imports. Known reserves are sma