iagara Falls.

GEOLOGIC FEATURES

The mineral graphite is a soft, steel-gray, crystalline form of carbon.

Ceylon graphite occurs in veins and lenses cutting gneisses and
limestones. Usually the veins consist almost entirely of graphite, but
sometimes other minerals occur in important amounts, especially pyrite
and quartz. The association of graphite with these minerals, and also
with feldspar, pyroxene, apatite, and other minerals, suggests that the
veins are of igneous origin, like some of the pegmatite veins in the
Adirondacks of New York. The graphite is mined from open pits and
shafts, and sorted by hand and mechanically. The product consists of
angular lumps or chips with a relatively small amount of surface in
proportion to their volume.

In Madagascar the graphite is mainly disseminated in a graphitic schist,
though to some extent it is present in the form of veins and in gneiss.
Most of the graphite is mined from a weathered zone near the surface,
and the material is therefore soft and easily concentrated. The product
is made up of flakes or scales, and in the making of crucibles requires
the use of larger amounts of clay binder than the Ceylon graphite.

The flake graphite of the United States, principally in the Appalachian
region, occurs in crystalline graphitic schists, resulting from the
anamorphism of sedimentary rocks containing organic matter. Certain beds
or zones of comparatively narrow width carry from 3 to 10 per cent of
disseminated graphite. The graphite is recovered by mechanical processes
of sorting. The graphite is believed to be of organic origin, the change
from organic carbon to graphite having been effected by heat and
pressure accompanying mountain-building stresses. Some of the graphite
also occurs in pegmatite intrusives and adjacent wall rocks. This
graphite is considered to be of inorganic origin, formed by the breaking
up of gaseous oxides of carbon in the original magma of the pegmatites.
The Montana graphite is similar in origin. This inorganic graphite in
pegmatite veins resembles Ceylon graphite, in breaking into large lumps
and chips, but supplies are very limited.

Amorphous graphite is formed in many places where coal and other
carbonaceous materials have undergone extreme metamorphism. It
represents simply a continuation in the processes by which high grade
coals are formed from plant matter (pp. 123-127). The Mexican deposits
are of this type, and occur in beds up to