GEMS AND PRECIOUS STONES. 661
A
new beryl prospect was opened in 1913 on the old Porter K. Filbert
farm, 1.5 miles S. 75° W. of South Danbury, in the town of Wilmot, N. H.
The work was done by J. E. Lovering, of Grafton, N.H., for
Charles Murphy, of Detroit, Mich., the present owner. The deposit is on
the west end of an elongated rounded hill about 200 feet higher than
the road on the west. At the time of examination the pegmatite had been
stripped of soil covering for about 200 feet and small prospects had
been blasted out. The country rock is chiefly coarse porphyritic
biotite gneiss which strikes northeast with a variable but high
southeast dip. This gneiss is cut by a medium-grained granite, and the
gem-bearing pegmatite cuts both rocks near their contact. The pegmatite
strikes about N". 75° E. and has a nearly vertical dip. Through most of
the exposed parts the pegmatite varies from 6 inches to 2 feet in
thickness, but in one place it bulges to nearly 8 feet in thickness.
The texture is fairly coarse, potash feldspar cryst als up to 8 inches
thick being observed. Much of the quartz is smoky gray, and some occurs
crystallized along with small albite crystals in pockets. Black
tourmaline and muscovite are other minerals associated with the beryls.
The beryl crystals occur unevenly distributed through the pegmatite.
They range from small size up to more than 2 inches in diameter. Most
of the crystals are opaque or translucent yellowish green, pale green,
or good aquamarine in color, but some clear gem crystals are found. Mr.
Lovering reported finding a crystal nearly 2 inches in diameter and
containing some aquamarine of gem quality.
A
small prospect has been opened for feldspar and beryl on Stuart Hill, 3
miles southeast of Grafton, in the town of Willmot. This hill is called
Severance Hill on Hitchcock's Atlas of New Hampshire. The hill is
composed chiefly of course porphyritic biotite gneiss which strikes
about north with an east dip. A large pegmatite cuts across the north
end of the hill forming a small cliff or break in the hill slope. The
south contact of the pegmatite with the gneiss approximates east and
west, with many minor irregularities. The pegmatite is of very uneven
grain which ranges from coarse, with potash feldspar crystals 4 feet
thick, down to a texture resembling coarse granite. A dike of
medium-grained granite cuts the porphyritic gneiss and the pegmatite
into which if appears to merge. Among the minerals observed in the
pegmatite, besides feldspar and quartz, were black tourmaline,
muscovite and biotite mica, and beryl. The beryl was rather plentiful
in crystals ranging up to 4 inches in diameter. They were
aquamarine-colored, yellowish-green, and yellow, but mostly opaque or
translucent. A few pieces nearly clear enough for cutting into small
faceted gems were observed and some of the translucent
aquamarine-colored would serve for cabochon gems.
Gem
beryl has been found at the Island mica mine, 2 miles N. 20° E. of
Gilsum, N. H. During the course of mica mining a large number of beryl
crystals and fragments, some of which contained gem material, were
thrown on the dumps. The dumps have since been picked over by
collectors and the best beryl removed. The mine was worked by three
open cuts and a short tunnel. Two of the open cuts were at the east
foot of a small knoll (glacial "roche moutonee") standing about 25 feet
above the surrounding swampy ground. These open cuts were 20 and 25
feet deep, respectively, but are now filled with water. The third cut
was made back into the knoll at a
