to the United States. Several thousand
tons are produced yearly in Germany and France, and are largely consumed
there.

The production of fluorspar in the United States is several times that
of any other country. The ore mined comes principally from the southern
Illinois and western Kentucky field, and is used largely for fluxing
purposes in open-hearth steel furnaces. Minor amounts are produced in
Colorado, New Mexico, and other states.

The United States has sufficient supplies of fluorspar to meet all its
own demands for this material. Small amounts, however, are imported for
use in eastern furnaces because the material can be brought over from
England very cheaply. The domestic fluorspar is suitable for practically
all purposes for which fluorspar is used except for lenses in optical
instruments. For this use very small quantities of material imported
from Japan have been used, but recently fluorspar of a grade suitable
for optical purposes has been found in Illinois, Kentucky, New
Hampshire, and other states. For fluxing purposes domestic fluorspar is
superior to the foreign product.

GEOLOGIC FEATURES

Fluorspar is the trade name for the mineral fluorite, which is composed
of calcium fluoride. This is a common mineral in veins and replacements
which carry ores of zinc, lead, silver, gold, copper, and tin. It is
formed under a variety of conditions, but is always ascribed to
solutions coming from nearby igneous rocks.

The large fluorspar deposits of Illinois and Kentucky contain fluorite
with calcite, barite, and metallic sulphides, in wide veins filling
fissures in limestones and sandstones and replacing the fissure walls.
Into these sediments there are intruded certain peridotite dikes. The
fluorite and associated minerals were probably deposited by hot
solutions bringing the material from some large underlying igneous mass
of which the dikes are off-shoots.

In the western United States many metalliferous deposits carry large
amounts of fluorite, which is treated as a gangue or waste mineral, but
which could be profitably extracted if there were local markets. In
England, fluorite is obtained in this manner as a by-product from lead
and zinc mines.

SILICA

ECONOMIC FEATURES

Silicon and its oxide, silica, find important applications in the
manufacture of iron and steel. Silicon, like manganese, is an important
constituent of many steels, the alloy ferrosilicon being added to
deoxidize and pu