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PRECIOUS STONES.
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827
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The
larger garnets are now difficult to obtain; but it is probable that the
"Arizona ruby" will again become more plentiful when the Indian learns
to work a little more systematically for this gem.
COLORADO.
J.
D. Endicott, of Canon City, Colo., has taken up two claims for garnets
on Grape Creek, 2 miles S. 75° W. of Canon City. The country rock is
biotite schist-gneiss, garnetiferous in streaks. It strikes north of
east to east and west and dips 45° N. Pegmatite is associated with the
gneiss in places. The portion prospected for garnets consists of a
garnetiferous streak in which the garnets are rather plentiful and of
some size. Certain smaller bands and lenses in the "vein" up to 8 or 10
inches thick are richer in garnets than the rest of the rock. The
garnets are found in crystals varying from minute size to over 3 inches
in diameter, wrapped in biotite in the gneiss. The greater part of the
garnets are more or less crushed and fractured. The cutting material,
though mostly small, comes from the solid portions of the crystals not
injured by fracturing. The color is the beautiful red to pinkish red of
almandite or precious garnet, and handsome gems of about 2 carats'
weight have been cut.
Specimens
of spessartite garnet and topaz are still obtained from Ruby Mountain
on the east side of Arkansas River opposite Nathrop, Chaffee County,
Colo. The deposit is on public land and is visited intermittently by
collectors chiefly for mineral specimens, though some garnets suitable
for cutting are obtained. The work done by each collector does not
usually exceed a few blasts in the most favorable places. The locality
has been described by Whitman Cross,a and the following notes are prepared principally from his description:
The
garnets and topaz occur in cavities in a rhyolite of probable Tertiary
age. The rhyolite outcrops in three places—in Ruby Mountain, a hundred
yards north of Ruby Mountain, and on the west side of the river
opposite Ruby Mountain. Ruby Mountain is a hill about 200 feet high and
a quarter of a mile long, running north of west and east of south
parallel with the course of the river. The upper and larger part of the
hill is composed of white to pinkish-gray rhyolite of very fine grain
with more or less flow banding of light and darker laj'ers. The lower
portion of the hill where outcrops are not covered with talus on the
southeast and northwest ends are composed of gray volcanic glass with
perlitic texture. This perlite contains numerous round particles of
obsidian up to the size of a pea. On the east side of the hill are
rhyolitic tuff beds which, in an exposure on the north of the hill, dip
about 20° E. Cross mentions vertical contact between the rhyolite and
inclosing Archean gneiss.
The
crystal-bearing cavities are larger and more abundant in the rhyolite
in the upper part of the hill. These cavities are lithophysae as in the
Utah topaz locality described later. The cavities range in size from a
millimeter cross section to more than 5 centimeters in greatest
dimensions. They are elongated in the direction of the flow lines in
many places or are composed of numerous smaller joining cavities in
this direction. Some of the lithophysae shells are fairly
o Topaz and garnet In rhyolite: Am. Jour. Sci., 3d ser., vol. 31, 1886, pp. 432-438.
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