104 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
its
solidification. Microscopically the effects of these movements are
recognizable in local granulation within certain quartz and feldspar
individuals and marked strain in others.
The
coarsest portions of the pegmatite have been worked for mica. A few of
the muscovite books are as much as 1 foot across, but the majority are
under 4 inches. The larger plates are only in part clear, being injured
by ruling and twinning. The writer saw no plates that would cut clear
pieces larger than 2 by 3 inches, and even such as would were rare.
Most of the material could be utilized only for scrap mica. The
property hardly appears to merit further development.
Beech Hill mica mine.—Another
mica mine, located a Tew miles north of the first, on the farm of
George L. Kimball, on Beech Hill, represents the most serious attempt
at mica mining that has been made in the State. The mica occurs as a
constituent of a sill-like mass of coarse pegmatite, which dips to the
east at about 30°. Its thickness is at least 12 feet, the base not
being exposed. Commercial mica is confined to a zone about 5 feet
thick in the lowest part of the pegmatite layer as now exposed. Within
this 5-foot zone muscovite is estimated to form from 10 to 20 per cent
of the material of the pegmatite.
Some
of the masses of pure orthoclase feldspar associated with the mica are
5 feet across, but the total quantity present is not sufficient to make
it of commercial importance. Intergrowths of quartz and muscovite are
common.
The
pegmatite contains no biotite and no black tourmaline. The associated
rock is a granite gneiss, and both gneiss and pegmatite are intruded by
a dike of diabase.
Some
of the muscovite books are 1 foot across, but most of them are under 5
inches. The larger plates are invariably cut up by ruling planes into a
number of smaller pieces. Much of the mica is worthless for anything
but scrap because of the prevalence of ruling, wedge structure, and
twinning. Most of the thumb-trimmed material seen by the writer was in
pieces 2 or 3 by 3 inches in size. The mine was not being worked at the
time of the writer's visit in September, 1906, and although several
tons of mica lay in the trimming sheds, the best of the output was
reported to have been sold. It was therefore impossible to make a
wholly fair estimate of the average value of the mica mined, but the
quality of the material is superior to that from any other known
locality in Maine and appears to warrant further development.
The
property was opened in 1900 and was also worked in 1902 by the Beech
Hill Mining Company, who subsequently sold the property to New York
persons. About a ton of thumb-trimmed mica was marketed at prices
ranging from S cents to SI a pound, and
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