52 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
in
graphic intergrowths with quartz. As described below, some, small clear
muscovite prisms are surrounded by a border of lepidolite. Mr. Lamb has
also found some fine curved crystals of muscovite.
Biotite
is abundant only locally and can in most areas be readily avoided in
mining the feldspar. It forms typical lath-shaped crystals.
Lepidolite
is not very abundant, but some occurs especially associated with
clevelandite and muscovite near pockets. It is present in granular
aggregates of small plates and prisms (in many places intergrown with
some quartz) and also in larger plates. Its occurrence as narrow
borders surrounding muscovite and in crystallo-graphically parallel
growth with it has been fully described and figured by Clarke,a who gives analyses of both of the muscovite and the lepidolite border.
Garnets
of small size occur sparsely in all parts of the pegmatite. They are
most abundant in the more quartzose and micaceous parts and are not
present in injurious amounts in the more highly feld-spathic portions.
Black
tourmaline is present in all those portions of the pegmatite which
carry colored tourmalines but is only locally abundant and is not
particularly bothersome in feldspar mining. Most of the colored
tourmalines which have been obtained have come, not from the feldspar
workings, but from small pits near the Hatch farmhouse, worked at an
earlier date solely for their gems and mineral specimens. Those found
in 1883 by N. H. Perry ranged from 1 centimeter to 10-1/2 centimeters
long, and differ from the majority of the Maine tourmalines in being
mostly of lighter color. They were found colorless, light pink, lilac,
light blue, light puce colored, bluish pink, and light green, some
single crystals showing nearly all these colore. Gems from some of the
paler crystals are said to have deepened very much in color after
cutting. The majority of these crystals, of which nearly 1,500 were
obtained, were more or less flawed. Some of the tourmalines found later
by Mr. Lamb were cut into gems of emerald-green color.
Crystals
of light bluish-green beryl also occur rather abundantly, embedded in
the solid pegmatite. One hexagonal beryl found about 1898 is reported
by J. S. Towne to have been 4 feet in diameter and 20 feet in length,
but the majority do not exceed 1 foot in length and a few inches in
diameter. Near the gigantic beryl mentioned occurred several pockets
bearing the finest crystals of herderite ever found on Mount Apatite;
the form and composition of these have been described by Penfield.6
Apatite
occurs occasionally in crystals of fine luster and trans-parency, the
colors being light pink, purple, light blue, and blue
