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GEMS AND PRECIOUS STONES. 317
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end
of the hill, one in flat ground to the west and at the foot of the hill
slope, another 100 yards northeast on the hill slope, and the third
about 200 yards east also on the hillside. Horse Hill is composed of
granite gneiss inclosing beds of mica gneiss, both of which are cut by
pegmatite. The lower prospect to the west consists of an exposure of
pegmatite 75 feet across, outcropping somewhat like a floor. Only the
southeast wall is exposed, and this strikes N. 35° E. with a northwest
dip. The pegmatite contains irregular quartz segregations, orthoclase
crystals 1 foot across, greenish muscovite, and beryl crystals. The
beryls range up to 2 inches in diameter and are mostly opaque. Some of
the beryl is transparent and rather pale aquamarine green.
At
the prospect 100 yards to the northeast a pegmatite vein 18 inches to 3
feet thick crops out in a direction S. 60° E. around the end of the
hill for a distance of nearly 100 yards. The vein cuts the bedding of
the granite and inclosed gneiss which strike N. 30° E., with a high
west dip. Beryl crystals are plentiful in the northwest end of the
outcrop.
At
the east prospect a pegmatite ledge 2 to 6 feet thick with a low
northwest dip outcrops in a northeast direction around the hillside.
Many loose blocks of pegmatite and quartz have rolled down the hill
slope below. Good beryl crystals have been found at this locality, some
being of clear aquamarine color. One rough crystal was found which
would cut into a gem weighing possibly 10 carats.
At
the Keene granite quarry rock has been quarried over an area about 150
yards long in a northeast direction and about 100 yards wide. The
granite is a fine to medium grained gray muscovite-biotite variety. On
the southeast side of the quarry a vein of pegmatite cuts the granite
with a strike of N. 55° E. and a vertical dip. The pegmatite forks into
streaks, which pinch out or enlarge irregularly. The pegmatite
contains gray to smoky quartz segregations, crystals of microcline or
anorthoclase 2 or 3 inches thick, muscovite crystals 1 to 2 inches
across, black tourmaline thickly intergrown with
3
quartz, a little
biotite, and beryl crystals. The beryls range from dark to pale golden
to greenish yellow to yellowish green in color. Most of them are small,
but a large proportion contains parts clear enough to cut. The cut gems
are very brilliant, and some of the greenish-yellow stones are
unusually pretty.
A
deposit was operated for mica and gem beryl several years ago by
Franklin Playter, of Boston, in the town of Springfield, Sullivan
County, N. H. It is on one of the higher summits of Springfield
Mountain (called Melvin Hill on Hitchcock's Atlas of New Hampshire), 3
miles S. 40° W. of Grafton, at an elevation of 2,100 feet above sea
level. The workings consist of four open cuts along a small ridge.
Three of the openings fall in a line of about N. 55° E., within a
distance of 150 feet on the northwest side of the ridge, and the fourth
is about 100 feet southeast on the opposite side of the small ridge.
Two of the open cuts are 25 feet across and are connected by a passage
6 feet wide. The different openings vary from 8 to 25 feet deep.
The
country rock is muscovite-biotite gneiss, which has a general northeast
strike and high southeast to vertical dip. The pegmatite cuts the
gneiss irregularly with its greatest length corresponding
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