and
their principal dark-colored constituents black mica (biotite) and
black tourmaline. In pegmatites in which black mica is abundant black
tourmaline is almost always rare or absent, and vice versa. Accessory
constituents present in almost all pegmatites are garnet, magnetite,
and green opaque beryl. Accessory minerals present only in certain
pegmatites number over fifty species, the most important probably being
lepidolite or lithium mica; amblygonite; spodumene; blue, green, and
pink tourmaline; transparent green, pale-blue, or golden ber}d;
colorless to amber-colored topaz; and rose and amethystine quartz.
The following minerals have been reported from the pegmatite deposits of Maine:
Albite.—Common
in many of the pegmatite deposits; in some places massive, but usually
occurring as the white lamellar variety clevelandite. Especially
abundant in gem-bearing pegmatites.
Allanite.—Reported from pegmatite at Mount Apatite, in Auburn.
Amblygonite.—An original constituent of many of the pegmatite deposits, especially those bearing gem minerals.
Apatite.—Occurs
as an original pegmatite constituent wholly inclosed by other minerals
in many pegmatite deposits. The fine purple apatites «f Mount Apatite,
in Auburn, occur on the walls of pockets and were probably deposited by
aqueous or pneumatolytic agencies during the latest stages of the
pegmatite crystallization.
Arsenopyrite.—Reported from pegmatite at Mount Rubellite, in Hebron.
Autunite.—Occurs
at the Dunton tourmaline mine in Newry, Oxford County, in crystals
seldom over ^ inch across, embedded in or lying between plates of
clevelandite. Mostly decomposed. Found also at Harndon Hill, in
Stoneham.
Bertrandite.—Occurs with herderite and hamlinite in cavities in pegmatite at Stoneham.
Beryl.—Translucent
to opaque varieties, wholly inclosed by other constituents, occur in
nearly all the coarser pegmatite bodies. A few crystals reach gigantic
proportions. In a few coarse pegmatites transparent pale-green gem
varieties (aquamarine) occur completely embedded or projecting from
the walls of cavities.
Beryllonite.—Not
found in place, but occurring in the soil in Stoneham. It is attached
to typical pegmatite minerals and is plainly an original pegmatite
constituent.
Biotite.—One of the abundant constituents of most of the pegmatites.
Calcite.—Not observed as an original pegmatite constituent, but occurs occasionally as a secondary deposit in fissures and cavities.
Cassiterite.—An original constituent in pegmatite at Paris, Hebron, Stoneham, and Auburn.
Childrenite.—Reported
as an original constituent of pegmatite at Mount Rubellite, in Hebron,
occurring in minute hair-brown prismatic crystals with amblygonite.
Chrysoberyl.—An original pegmatite constituent at a large number of localities, though nowhere abundant.
Clevelandite.—See Albite.
Columbite.—An original constituent of certain pegmatites. Present only in small amounts.
Cookeite.—Abundant
as a coating in most of the pockets in the coarser pegmatites. Not an
original constituent but secondary and due to water deposition.
Damourite.—Occurs at Mount Rubellite, in Hebron, as an alteration product of tourmaline. Also reported from Mount Apatite, in Auburn.
