colorless
and occurs in books, some of which are 8 to 10 inches in diameter. The
great bulk of the muscovite is of the wedge variety and shows twinning;
it could be utilized commercially only as scrap mica. A small amount is
plate mica and splits readily into sheets, which when trimmed may
measure 4 by 5 inches, though mostly smaller. Most of this plate mica
incloses between its lamellae thin branching crystals of magnetite. A
few small masses of columbite, generally exhibiting very imperfect
crystal forms, are found in the quartz-feldspar masses.
The
wall rock of schist or gneiss is nowhere exposed at this quarry, and
the soil covering makes it impossible to trace the exact limits of the
deposit. If one may judge from neighboring masses of pegmatite whose
boundaries are exposed, this mass is probably more or less irregular in
outline and somewhat elongate in a direction parallel to the trend of
the neighboring schists—that is, somewhat east of north. The deposit
does not appear to be very extensive, but the quality is good, and
there seems to be warrant for further development work on a small scale.
A
second small feldspar quarry, on the northern slope of Mount Ararat,
consists of a single hillside pit about 150 feet long, 30 feet in
average width, and 20 feet in greatest depth. It was last worked in
1905. The rock is a wholly irregular association of quartz, feldspar,
muscovite, biotite, and garnet, with smaller amounts of rarer minerals.
The quartz is prevailingly dark gray in color and semiopaque, but in
some places is white and in a few nearly black. A number of the pure
quartz masses are 3 to 4 feet across; one, flat lying and exposed at
the base of one of the quarry walls, is 5 feet in maximum width and 25
feet in length, with very irregular boundaries.
Most
of the feldspar is pale pink in color, but certain portions are cream
colored, and others decidedly red. Microscopic examination shows that
the feldspar belongs mainly to the potash varieties ortho-clase and
microcline, the former greatly predominating. With these are associated
small amounts of the soda feldspar, albite, which is frequently
intergrown microscopically with the orthoclase or mieroeline.
Throughout most of the quarry the masses of pure feldspar are not over
4 to 5 inches across, though a few crystals measure 2 to 3 feet. The
bulk of the material quarried for pottery use is a graphic inter-growth
of feldspar and quartz, most of it coarser than that found at the
quarry on the eastern slope of Mount Ararat. The quartz thus intergrown
with the feldspar commonly assumes branching or dendritic forms, a
characteristic not observed in most of the pegmatite deposits.
Muscovite
of the wedge variety occurs sparingly in books up to 6 inches in
greatest diameter. No clear plate mica was observed. Of very common
occurrence are graphic intergrowths of muscovite
