in
the same piece is not uncommon, especially in mottled matrix, as bright
blue spots or lines in paler turquoise. The mineral halloy-site is
associated with turquoise in olive-green and grayish masses and in
nugget form similar to turquoise nuggets. Halloysite is opaque to
translucent and has a waxy luster. When moist and fresh from the mine
the halloysite has about the consistency of candle wax. It hardens and
cracks on exposure to the air, however, though it does not become so
hard as turquoise. Among numerous associations the following were
noted: Pale-blue vein turquoise with a network of yellowish-brown
hydrous aluminum phosphate streaks; blue-white vein turquoise
containing open cracks and streaks of darker material; light-blue vein
turquoise containing yellow spots of phosphate, quartz grains, and
darker veinlets of purple and blue parallel to the walls.
The
turquoise from the Elizabeth pocket is probably the finest ever found
in the world. Much of it is of a deep blue color, slightly translucent,
and over 6 in hardness, so that it makes a fine wearing gem. The cut
gems of good quality from the Azure mine are marked with a circle on
the lower side, and such stones are guaranteed to hold their color for
a number of years or to be replaced. Mr. Zalin-sky states that the
Azure mine has produced turquoise to the value of several million
dollars since 1891.
Mr.
Zalinsky suggests that the turquoise was formed in the vein where
copper-hearing solutions, rising in fissures with a northwest dip,
crossed phosphate-bearing solutions rising in fissures parallel to the
vein with a southeast dip. In support of this theory the occurrence of
such copper minerals as malachite and chrysocolla in the copper
fissures above the supposed phosphate fissures is cited. It is thought
the phosphoric acid of the turquoise was derived from the decomposition
of apatite in the original granite and the alumina from the
decomposition of the feldspar of the same rock. Where copper was
supplied in excess, the turquoise runs toward green in color. The
proper proportion of copper gives the best bright blue gem of greater
hardness than where the copper was not present in sufficient quantity.
In the latter case the turquoise is of pale color and inferior
hardness, and apparently this variety grades into simple phosphate of
aluminum.
American Gem and Turquoise Company mines.—The
operations of the American Gem and Turquoise Company were upon the
deposits in the Parker mine and near the prehistoric workings about 200
yards to the northwest. At the latter place the recent work consists of
two tunnels, of about 50 and 60 feet in length, driven in from a small
open work at the outcrop on a hillside. One of these tunnels running
southwest followed prominent seams, which carry turquoise in places
and dip about 50° to the southeast. The other tunnel cut across the
direction of the prominent seams and appeared to be exploratory work.
The country rock is typical quartz porphyry with prominent glassy
quartz phenocrysts and badly kaolinized feldspar crystals.
Mining
at the Parker mine was accomplished principally by open cuts, of which
two are fairly large. The one to the north was made in a gully running
east, and is nearly 100 yards long and 10 to 25 feet deep. The country
rock is hard quartz porphyry like that near the prehistoric workings. A
number of seams carrying turquoise cross
