is magnesium carbonate. The principal magnesite deposits are of
two types, of different modes of origin and of somewhat different
physical characteristics.

The large magnesite deposits of Austria and of Washington, as well as
those of Quebec, occur as lenses in beds of dolomite (calcium-magnesium
carbonate). They are in fairly close proximity to igneous rocks, and
magnesia-bearing solutions issuing from these rocks are believed to have
dissolved out the calcium carbonate of the dolomite and replaced it with
magnesium carbonate. In these deposits the material is coarsely
crystalline and forms fairly large, continuous bodies, which are worked
by quarrying. The Washington deposits closely resemble marble, and had
sometimes been mistaken for that rock until war-time needs resulted in
their more thorough investigation.

The commoner type of magnesite deposits is represented by those of
Greece, California, Venezuela, and many other countries. These consist
of veins and replacements in serpentine. The original rock was a highly
magnesian igneous rock of the peridotite type, which is very unstable
under weathering conditions, and rapidly alters to serpentine. Magnesite
is formed both by this process and by the further breaking down of the
serpentine itself. The processes are those of katamorphism. Under these
circumstances the magnesite is characteristically fine-grained or
massive, and occurs in veins, lenses, and irregular bodies in cavities
and fractured zones. It is usually worked by open cuts.

Magnesite is also reported to occur in sedimentary beds in which it was
primarily deposited in its present form and has not undergone later
alteration. Such deposits are not important commercially.

FLUORSPAR

ECONOMIC FEATURES

The chief use of fluorspar is as a flux in the manufacture of
open-hearth steel. Minor uses are in chemical and enameling industries,
in the smelting of copper, lead, and iron, and in the manufacture of the
ferro-alloys in the electric furnace.

In order to be used in steel-making, the fluorspar after being
concentrated should contain at least 85 per cent calcium fluoride and
less than 4 per cent silica. Chemical and enameling industries require
material with 95 to 98 per cent calcium fluoride and less than 1 per
cent silica.

The chief foreign producer of fluorspar is Great Britain, and much of
this product comes to the United States. Canada produces a small
amount, some of which also comes