_Amethyst_ (violet to purple-colored quartz).—A northeastern Gillespie
County locality known as Amethyst Hill has produced quite a number of
fine light to medium violet amethyst crystals which occur in quartz
veins and geodes associated with serpentine and talc. Many crystals have
been found loose in the soil.
The amethyst tends to be very irregularly colored in zones parallel to
the crystal faces. In many, the base of the crystal is colorless or
white and only the termination is violet. Crystals up to 3 inches long
have been found at this locality, but the average size is much less.
The surface at this locality is almost entirely depleted of amethyst,
with only an occasional small crystal or fragment to be seen. However,
small excavations are still sometimes productive.
Good groups of pale amethyst crystals have been found in quartz veins
near the old town site of Oxford, Llano County. The occurrence seems to
be much the same as the Amethyst Hill locality. Little exploration for
gemstones has been done in this area, and future discoveries seem
likely.
Chalcedony geodes lined with amethyst crystals have been found in
Brewster, Presidio, Culberson, and Hudspeth counties, but the
occurrences are scattered. The crystals are seldom large enough to yield
gems of more than 3 carats and are mostly very light colored.
A few pieces of gem-quality amethyst have been found in Burnet County.
_Citrine_ (yellow quartz).—Very little gem-quality citrine has been
reported in Texas. Some small citrine crystals have been found at
Amethyst Hill in northeastern Gillespie County, but few are of
sufficient size or color to yield good gems.
The writer has seen one citrine crystal that was found in the gravels of
a small stream in eastern Llano County near Buchanan Dam. The crystal
weighs about 1 ounce and is perfectly clear, light golden yellow, and
flawless. However, a further search of the stream gravels failed to
produce any other citrines.
_Rock crystal_ (colorless quartz).—Numerous localities in Texas produce
this colorless variety of quartz, which is the most common variety of
facet quality quartz and consequently is of little value.
Rock crystal occurs at many localities in Burnet, Llano, and Mason
counties. The crystals mostly occur in pegmatite dikes or in stream
gravels where they have been weathered out of their parent rock. Some
fine colorless quartz crystals have been found near Voca, Mason County,
in weathered pegmatite dikes and also loose in the sands of nearby
streams. Crystals from this locality are often stained with reddish iron
oxide on their outer surfaces. Some of the rock crystal found near
Katemcy, Mason County, shows asterism when cut with the proper
orientation. Fine clear colorless crystals up to 8 inches long have been
found in the pegmatite dikes near Lake Buchanan in both Llano and Burnet
counties. Several localities near Enchanted Rock in Llano County have
also produced some good colorless crystals.
Feldspar quarries in large pegmatites in northeastern Gillespie County
have yielded attractive quartz crystals, some of which contain smoky
phantom crystals and tourmaline inclusions.
Some pieces of rock crystal enclosing green, needle-like actinolite
crystals have been found near the Llano-Gillespie-Blanco County corner.
This material is not suitable for faceted gems but does lend itself to
interesting and attractive cabochons.
Colorless quartz crystals commonly are found lining small chalcedony
geodes in Brewster, Presidio, Culberson, Hudspeth, Reeves, and Jeff
Davis counties. These crystals are most commonly less than 1 inch long
but are mostly very clear.
Rock crystal has been found in crevices of petrified wood in many east
and southeast Texas counties, although the crystals are mostly quite
small.
Many lesser occurrences of rock crystal, too numerous to mention, are
located within the State.
_Rose quartz_ (pink quartz).—Rose quartz occurs at various localities in
Burnet, Llano, Mason, and Gillespie counties, but the amount of material
is mostly small and the greater part unsuitable for gem purposes. Some
good pink rose quartz occurs near Town Mountain, Llano County, but this
material does not have flawless areas large enough to yield faceted
stones of more than a few carats. Rose quartz is always slightly milky,
or cloudy, and does not cut into brilliant faceted stones. The Town
Mountain rose quartz has been cut into attractive cabochons.
_Smoky quartz_ (brown, yellow-brown, and golden-brown quartz).—Several
Texas localities have produced fine smoky quartz. Baringer Hill, a noted
rare-earth minerals pegmatite locality in Llano County, contained some
smoky quartz crystals that were estimated to weigh over 1,000 pounds,
and the locality produced many smaller crystals that were of gem
quality. Baringer Hill was flooded by the completion of Buchanan Dam in
1938 and is presently under the waters of Lake Buchanan. A few fine
golden-brown gem-quality crystals have been found along the lake shore
and in small pegmatites nearby (Pl. III, B.).
Feldspar quarries in northeastern Gillespie County have produced smoky
quartz crystals that exceed 1 foot in length, but these crystals are
mostly flawed, possibly as a result of blasting, and mostly contain only
small clear areas.
Good color smoky quartz crystals are found with topaz in the pegmatites
and stream beds in Mason County, near Streeter, Grit, and Katemcy. These
crystals tend to be lighter colored than those near Lake Buchanan, but
they commonly contain large flawless areas.