88 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
cross each, other with mutual penetration about at right angles, but most commonly several crystals diverge from single points, forming fan-shaped aggregates extending through 60°, 90°, or even 100°.
None of the above-described tourmalines are of gem value.
Amblygonite
is the only other mineral occurring at all abundantly in the pegmatite.
It is found only as a constituent of the solid pegmatite in irregular
masses often 4 to 8 inches across. One mass is estimated to
have weighed nearly 800 pounds. The mineral usually occurs near the
pockets and is regarded as an indicator of their proximity.
Spodumene
occurs in opaque gray flat crystals, usually associated with
lepidolite. One crystal measured 2 feet long, 7 inches wide, and 2
inches thick. Portions of a few of the crystals are a transparent pale
blue or pink. According to Mr. Merrill, an abundance of beryl or
spodumene about a pocket generally signifies that the latter contains
few if any tourmalines. A white spodumene. crystal in the Hamlin
collection at Paris is 7 inches long and 4 inches thick and is split by
a wedge-shaped mass of granular lepidolite tapering from 1 inch to
one-half inch in thickness.
Apatite
occurs in the solid pegmatite in irregular opaque green masses, some
few of which weigh a couple, of pounds. A small deep-blue bipyramidal
crystal one-fourth inch in length with crystal faces developed in
remarkable perfection has been described and figured by Prof. E. S.
Dana.®
Cassiterite
occurs rarely, usually associated with clevelandite near the pockets.
Some crystals are found embedded in the sandlike materials at the
bottom of the pockets.
Columbite is rare and usually occurs in irregular bladelike crystals.
Arsenopyrite
was observed in veinlike masses, mostly one-eighth to one-fourth inch
in width and 2 or 3 inches in length, flanked by irregular borders of
quartz, which in turn are irregularly bordered by orthoclase and
microcline. The arsenopyrite therefore virtually forms the central
portion of small contemporaneous quartz veins or lenses in the
pegmatite.
Triphyllite occurs mostly in aggregates, many of which weigh from 10 to 20 pounds and a few as much as 50 pounds.
Zircons occur mostly associated with triphyllite, few crystals being over one-eighth inch in diameter.
Kaolin
occurs in considerable amounts in the bottoms of some of the pockets as
a decomposition product of feldspar. In the giant pocket shown in Plate
XIV over a ton of the pink kaolin montmoril-lonite was aggregated at
one end of the pocket.
Other
minerals found at Mount Mica are autunite, brookite, chil-drenite,
damourite, halloysite, lollingite, petalite, pyrite, sphalerite,
