tosity
of the inclosing rocks. The latter with the interbedded pegmatite dip
at high angles in some places, while in others they are but gently
inclined. The dip of the formations has much to do with the regularity
of the surface outcrop. The latter is more regular and the deposits are
more easily followed where the dip is at a high angle than where it is
low. Other deposits have no definite direction, but resemble stocks in
form.
These
pegmatites represent one phase of the granitic intrusions, of late
Silurian or Devonian age, so abundant in southern and southeastern
Maine. They are intruded into metamorphic slates and schists, with
which are associated igneous gneiss, diorite, diabase, etc. Dikes of
fine-grained granite are generally associated with the pegmatites and
have been found grading into them. The texture of pegmatite varies
greatly in different deposits and in different parts of the same
deposits. Only those with coarser texture are worked for their
valuable minerals, such as feldspar, quartz, mica, and gem minerals.
Some of the deposits are worked for more than one of these. The gem
tourmalines are usually obtained from pockets in the pegmatite, while
the beryl is nearly always embedded in solid pegmatite.
The
color and quality of the gem minerals found are often very fine. The
tourmaline ranges from white or colorless through various shades of
blue, green, and red. One or more of these colors often appear in the
same crystal, either in more or less clearly defined layers across the
crystal or with one color as a core and others surrounding it. The
topaz varies from colorless to amber color, and some specimens from
Stoneham, Oxford County, have been described by Doctor Kunz as of
beautiful quality, transparent in parts and colorless or faintly tinted
with green or blue. Besides clear varieties of quartz, rose and
amethystine-colored varieties are found. Beryl in opaque crystals is
common, and some of gem quality is encountered, either aquamarine,
golden beryl, or rarely emerald. A colorless to bluish or pinkish-white
variety containing a small percentage of csesium is also found. These
stones, when not used for museum specimens, are generally cut by Maine
lapidaries and sold within the State, where they command a higher price
than they would in the open market. Most of the cut tourmalines sold
are under 3 carats in size. The Maine stones, like the tourmalines from
other localities, generally have to be cut with the table parallel to
the longer axis of the crystal, since the absorption of light is so
strong in colored stones in the direction of this axis that a stone
with a table at right angles to it appears dull and dark. The caesium
beryl makes a stone well adapted for evening wear, rivaling some
diamonds in brilliancy.
The following table represents the prices of flawless cut stones as sold in Maine:
