72 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
form.
Wherever the walls of this pocket have not "shelled off" by the action
of frost, etc., they are covered with a coating of minute crystals of
quartz. In some places the minerals which have been coated in this way
have subsequently decayed, leaving only their quartz covering. As these
quartz crystals are transparent and usually show hexagonal forms they
probably crystallized below 575° C, presumably as a deposition from
meteoric waters. Where this secondary quartz has been deposited on
original quartz crystals it has grown in perfect crystal continuity
with them but is distinguished by being opaque white rather than
transparent. It is interesting to note that this growth of secondary
quartz lias been most rapid at the apices of the quartz crystals, the
coating here being much thicker than on the sides of the crystals.
The
precise form and extent of the pegmatite deposit could not be
ascertained, but it appears to be irregular. The coarse pegmatite is
traceable for about 25 feet north of the present pit, beyond which it
is concealed by soil. The southern wall of the pit is composed of
schists, which strike N. 50° W. and dip nearly vertical.
The
locality has yielded a considerable number of tourmalines of gem
quality, but very few have been marketed, much of the material being
still in the hands of George Noyes, of Fryeburg, who developed the
property. Other minerals occurring here are apatite in small, opaque,
olive-green crystals (present in great abundance in some of the
fine-grained parts of the pegmatite), opaque, pale lilac-colored
spodumene, cassiterite, beryl, herderite," zircon, and phenacite.
The locality, though affording many interesting mineral specimens, can not be regarded as of much commercial importance.
HEBRON.
The
rocks of the town of Hebron are principally quartz-mica schists,
extensively intruded and injected by pegmatite, which shows great
variations in coarseness. The coarser phases have proved of economic
importance for feldspar at Number Four Hill in the western .part of the
town and on the Hibbs farm north of Hebron village, and gem tourmalines
and various mineral specimens have been obtained at Mount Rubellite,
about 2 miles northeast of Hebron village.
Hibbs feldspar and mica mine.—A small feldspar and mica mine was opened in 1906, about 1-1/2 miles
north of Hebron village near the Buckfield road. It is located on the
farm of Alton Hibbs and was operated during 1906 by J. A. Gerry, of
Mechanic Falls, and W. Scott Eobinson. It was abandoned in 1907. The
property was visited by the writer in August, 1906, after considerable
stripping and prospecting had been done. The ledge was exposed for a
distance of 300 to 350 feet along the southwest side of a small creek
valley, the
