many
plants were obliged to curtail or cease operations. The United States
has now about 40 per cent of the zinc-smelting capacity of the world.
For the present at least the capacity is far in excess of the domestic
requirements.

Before the war German control of the international zinc market was even
stronger than in the case of lead. The German Zinc Syndicate, through
its affiliations, joint share-holdings, ownership of mines and smelters,
and especially through smelting and selling contracts, controlled
directly one-half of the world's output of zinc and three-fourths of the
European production. It regulated the Australian exports by means of
long-term contracts, and had considerable influence in the United
States. To some extent it was able to so manipulate the market that zinc
outside the syndicate was also indirectly controlled. During the war
political jurisdiction was used by the Allied countries to destroy this
German influence.

In the United States the principal zinc-producing regions are the Joplin
and adjacent districts of Missouri, Oklahoma, Kansas, and Arkansas,
furnishing about one-third of the country's output; the Franklin Furnace
district of New Jersey, and the Butte district of Montana, each
yielding about one-sixth of the total supply; and the Upper Mississippi
Valley district of Wisconsin, Iowa, and Illinois, the Leadville district
of Colorado, and the Coeur d'Alene district of Idaho, each producing
between one-tenth and one-twentieth of the total. Smaller quantities are
produced in Tennessee, New Mexico, Nevada, and several other states.

Reserves of zinc are ample for the future. They are now developed
considerably in advance of probable requirements, a fact which causes
keen competition for markets and renders zinc-mining more or less
sensitive to market changes.

GEOLOGIC FEATURES

The most important mineral of zinc is the sulphide, sphalerite or "zinc
blende." The minerals of the oxide zone are smithsonite (zinc carbonate)
and calamine (hydrous zinc silicate), which yield minor amounts of zinc
and are especially productive at Leadville, Colorado. Zincite (zinc
oxide) and willemite (zinc silicate) are the important minerals in the
deposits of Franklin Furnace, New Jersey. The association of most
deposits of zinc with more or less lead has been noted.

The ores of zinc are of two general classes, corresponding to the two
classes of lead ores (pp. 211-212). Zinc ores of the first type a