Silver has many uses. Like gold, it is a beautiful metal that long has
been used for coins and ornaments. A large amount of silver goes to make
articles such as spoons, forks, platters, and trays. The photographic
industry uses silver—much of the film for cameras is coated with a
silver halide. Doctors and dentists use silver, too. The mixture that a
dentist uses to fill teeth contains silver along with several other
metals. Doctors sometimes use silver wire to fasten broken bones, and
silver compounds and solutions, such as silver nitrate, are used in some
kinds of medical treatment.
Perhaps more people have heard of legendary, lost silver mines of Texas
than of the actual and important silver deposits found in the
Trans-Pecos country of west Texas. Some of the west Texas silver
minerals include _argentite_, _cerargyrite_, and _native silver_.
Although the argentite and native silver commonly found there are mixed
with galena, a lead mineral, or with chalcocite, a copper mineral, they
also occur separately.
The element silver is found alone as _native silver_. When pure, it is
rather easy to recognize. It is metallic and has a silver-white color
that may tarnish to gray, black, or yellowish brown. Native silver is
heavy (it has a specific gravity of 10.5) and soft (a pocket knife
scratches it easily). When you rub it across a streak plate, native
silver, unless it is tarnished, leaves a shiny, silver-white streak.
This metal is so ductile that it can be drawn into a wire. It is also
malleable and flattens when hit with a hammer.
Silver occurs as crystals, which are poorly shaped cubes and
octahedrons, or as irregular masses. It may have a net-like appearance
(called _reticulate_), or it may be shaped like little needles
(described then as _acicular_). It occurs in wires (then called
_filiform_) or as scales or plates.
[Illustration: Prospector.]
Two of the Texas silver minerals, _argentite_ and _cerargyrite_, do not
resemble silver at all. _Argentite_, a silver sulfide, is also called
_silver glance_. It is a dark, lead-gray mineral with a metallic luster
that weathers to a dull black. When you rub it across a streak plate,
argentite gives a shiny, blackish to lead-gray streak. This mineral is
soft enough to leave a mark on paper. It has a specific gravity of 7.3,
and it is sectile enough to be cut smoothly (like soap) with a knife. In
some places argentite is found as irregular masses or as a coating on
rocks and other minerals.
Another silver mineral, _cerargyrite_ (or _horn silver_) is a silver
chloride. This mineral has a nonmetallic luster and is transparent to
translucent. It resembles pearl-gray, white, greenish, or colorless wax.
When exposed to the light it turns violet brown or black. Cerargyrite is
soft—you can scratch it with a fingernail. Like argentite, it is
sectile. This mineral has a specific gravity of 5.5, and it commonly
occurs as irregular masses and as crusts.
These silver minerals have been mined at a number of places in
Trans-Pecos Texas. The largest silver mine in Texas, the Presidio mine,
is located near Shafter in south-central Presidio County. It contains
argentite, cerargyrite, and native silver, along with galena and several
other minerals. This mine is not open now, but in the years between 1885
and 1942, it produced a large amount of silver along with some lead and
gold. There are several other lead-silver mines in this Shafter area,
but none has produced as much as the Presidio mine.
In this mine, the silver minerals occur mostly in large, flat deposits
in Permian limestone and other sedimentary rocks. The minerals are
believed to have been deposited there—probably during Tertiary time—by
solutions that came from hot magma far below the rocks. As they moved in
along the layers of limestone, the solutions replaced portions of this
rock with minerals containing silver, lead, and other elements. Later,
water seeped into these deposits and dissolved some of the minerals.
This dissolved material was then re-deposited, and it formed most of the
minerals we now find there.
No silver is being mined in Texas at present, but it has, in the past,
been produced from other Trans-Pecos mines. Galena that contains silver
(called _argentiferous galena_) has been mined at the Bird mine at
Altuda Mountain (about 14 miles east of Alpine) in northern Brewster
County. It also has been obtained from mines in the Quitman Mountains
and in the Eagle Mountains of Hudspeth County. Some cerargyrite has been
mined at the Plata Verde mine near the Culberson-Hudspeth County line.
Several mines in the Van Horn area of Culberson and Hudspeth counties
have produced silver along with copper. An important silver mine in this
area is the now idle and flooded Hazel mine. (This mine is described
with copper minerals on p. 52.)
Smoky Quartz. _See_ Quartz.
Soapstone. _See_ Talc and Soapstone.
Specular Hematite. _See_ Hematite.