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PEGMATITES AND ASSOCIATED ROCKS OP MAINE. 133
QUARTZ. GENERAL STATEMENT.
Quartz,
the most abundant of all minerals, occurs in nature in a great variety
of forms and is utilized commercially in many different ways. Sand
consisting mainly of quartz is used for building, molding, and in
glass and pottery manufacture. Tripoli, used for abrasive purposes,
and sandstone and quartzite, used for building and other purposes, are
also composed largely of quartz. The present discussion, however, deals
only with the massive crystalline and gem varieties which occur in the
pegmatite deposits.
Chemically
pure quartz is an oxide of silicon of the formula SiO,. ' It is too
hard to be scratched with a knife and will itself scratch glass. It is
generally translucent to transparent and ranges from colorless to dark
gray, and in the gem varieties from amethyst to pale pink. It is
brittle and without well-defined cleavage, fracturing irregularly with
lustrous glassy surfaces. Most of the quartz of the pegmatites occurs
in large pure masses without crystal outline. Quartz with crystal form
is developed principally in the pockets. The form of most of the
crystals is that of a six-sided prism terminated by an equal number of
faces forming a pyramid. The mineral is difficultly fusible and is
unaffected by acids under ordinary conditions.
MASSIVE CRYSTALLINE QUARTZ.
Occurrence.—Massive
crystalline quartz is usually white, but some is rose-colored or smoky.
It occurs in veins or dikelike masses, unmixed with other minerals, or
as a constituent of pegmatite. In the latter form it is usually
produced as an accessory in the mining of feldspar. The States
producing massive crystalline (vein) quartz in commercial quantity in
1908 were Connecticut, Maryland, New York, Pennsylvania, Wisconsin,
Tennessee, Montana, Colorado, and Arizona. Small quantities were
formerly marketed from Maine, but these quarries are so far from the
principal markets that there is very little profit in handling the
material. Quartz of excellent grade occurs in considerable quantities
at nearly all of the feldspar quarries of Maine and in a few is saved,
though not shipped regularly. It is allowed to accumulate in stock
piles until a favorable sale can be made.
The
Connecticut localities at which quartz is mined were described in
detail in the writer's report on the production of quartz and feldspar
in 1907.a The quarries of Westchester County, X. Y., have also been previously described by the writer.6
Milling.—In the grinding of the massive forms of quartz two general processes are used, the wet and the dry.
"
Mineral Resources U. S. tor 1907, pt. 2, U. S. Geol. Survey, 190s, pp.
84G-S47. » Bull. U. S. Geol. Survey No. 315,1907, pp. 294-309.
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