Among
the minerals associated with the peridot are garnet, emerald-green
diopside, quartz, calcite, titanic iron, and others. The garnets have a
beautiful red color, varying from deep pyrope-red to cinnamon-red, and
are mostly small, under 5 millimeters in diameter. Occasionally
garnets and diopsides of sufficient size to cut are found.
The
peridots display a large range of colors or shades of the same colors.
Some have a beautiful light yellowish-green color, others have richer
green or a stronger yellow tint. Some are a brownish green, and others
are regularly brown in color. Practically all are transparent and
clear, though some are slightly smoky or contain visible dust specks
through them. Under the microscope these dust specks appear as minute
hexagonal plates with a dirty brown color. Some peridots are clear
throughout, but contain a few scattered black spots. Others contain
minute cavities which appear on polished surfaces as tiny pits. A few
blades of an emerald-green mineral, probably diopside, were observed
inclosed in a peridot gem. Beautiful gems are cut from some of the
peridot from this region. Some of the perfectly clear golden-green
stones, so much admired, are obtained in gems of 3 to 4 carats weight.
Gems weighing from 1 to 2 carats are fairly abundant. The darker
yellowish-green stones could be obtained plentifully.
The
peridots occur in rounded and fragmentary grains with rough pitted
surfaces and some rather smooth cleavage faces. Some of the surfaces
are deeply pitted or corroded, as if attacked by the magma in which
they were contained. This corrosion is present on the peridot still
embedded in the peridotite agglomerate, and is therefore not caused by
later corrosion. The grains and specimens found range up to
three-fourths of an inch in larger diameter.
The
peridot region has been searched over so often by the Navajos that
large gems of rich yellowish-green color are difficult to find. Small
pebbles of peridot are abundant. It is probable that a large supply of
gems could be obtained by plowing or working up favorable areas of the
valley and allowing the rain to wash out the gems. Some of the soil is
dry and sandy, and in this it might pay to size off the pebbles with
sieves and then pick over for gems. This would have to be done without
water during the greater part of the year, as the stream bed in the
valley is dry.
QUARTZ, ROCK CRYSTAL, RUTILATED QUARTZ, ETC.
ARKANSAS.
Reports
of the discovery of diamonds near Delaney in Madison County appeared
during the year in the press. Specimens sent to the Survey by W. L.
Anderson, of Delaney, proved to be quartz of very clear limpid quality.
TEXAS.
J.
C. Melcher, of O'Quinn, Fayette County, reports that a number of the
clear colorless quartz pebbles found in that region were cut during
1908. Cut specimens sent to the Survey were perfectly clear and
colorless'and would be very satisfactory as souvenir gems.
