medicine, and in electroplating.

Practically the entire cadmium output of the world comes from Germany
and the United States. In addition, England produces a very small
quantity. Before the war Germany produced about two-thirds of the
world's total, and supplied the European as well as a considerable part
of the United States consumption. During the war the United States
production increased three to four fold, imports ceased, and
considerable quantities were exported to the allied nations in Europe
and to Japan. At present the United States is entirely independent as
regards cadmium supplies. Production is sufficient to supply all the
home demand and to permit exports of one-third of the total output. A
considerable number of possible cadmium sources are not being used, and
the production is capable of extension should the need arise.

GEOLOGIC FEATURES

Nearly the only cadmium mineral known is the sulphide, greenockite, but
no deposits of this mineral have been found of sufficient volume to be
called cadmium ores. Sphalerite almost always contains a little cadmium,
probably as the sulphide; and in zinc deposits crystals of sphalerite in
cavities are frequently covered with a greenish-yellow film or coating
of greenockite. These coatings have probably been formed by the
decomposition of cadmium-bearing zinc sulphide in the oxide zone, the
carrying down of the cadmium in solution, and its precipitation as
secondary cadmium sulphide. The zinc oxide minerals in the surficial
zone also are sometimes colored yellow by small amounts of greenockite.
In the zinc ores of the Joplin district of Missouri, cadmium is present
in amounts ranging from a trace to 1 per cent and averaging 0.3 per
cent.

Germany's cadmium is produced by fractional distillation of the Silesian
zinc ores, which contain at most 0.3 per cent cadmium. In the United
States there are large potential sources in the zinc ores of the
Mississippi valley, and considerable cadmium is recovered in roasting
them. Much of the American cadmium is also obtained from bag-house dusts
at lead smelters.

The general geologic conditions of the cadmium-bearing ores are
indicated in the discussion of lead and zinc deposits in an earlier
chapter.

COBALT ORES

ECONOMIC FEATURES

Cobalt finds its largest use in the form of cobalt salts, employed in
coloring pottery and glass and in insect poisons. Cobalt is also used in
some of the best high-speed tool steels.