Part 7

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.

CRYPTOCRYSTALLINE VARIETIES

Chalcedony.—When free from impurities of various oxides and other compounds, chalcedony has little to render it pleasing as a gemstone. It is mostly gray, white, brown, or bluish and commonly has a waxy luster. Some of the chalcedony found along the Rio Grande Valley and in west Texas will take dyes, and local lapidaries have had some success in dyeing this material various shades of blue, green, yellow, and red. When the chalcedony is naturally colored and variegated, usually in bands, mossy figures, or dendritic forms, it is called agate.

Agate (variegated chalcedony).—The wide variety of markings and colors available together with the ease of cutting make agate a favorite of many lapidaries. Fine agate has been found at numerous localities in west and south Texas. Fine plume agate, famous throughout the United States, is found south of Alpine. Plume agate is characterized by dendritic or tree-like inclusions and is mostly cut into very handsome cabochons. The agate from south of Alpine commonly contains black, red, yellow, or brown plumes within the same piece. The variety of colors and lack of porosity of this agate make it highly desired among lapidaries. The agate occurs loose on the surface of the ground and in the soil in small nodules that have a very rough, brownish surface. These nodules are mostly less than 3 inches in diameter, although specimens of gem quality have been found that exceed 200 pounds.

Some very fine agate has been found in the vicinity of Needle Peak, Presidio County. This material is mostly green moss agate in clear chalcedony and commonly contains small yellow “sun-burst” figures. The contrasting yellow and green design makes very beautiful cabochons.

Fine agate has been found south of Marfa, Presidio County. This agate is mostly clear chalcedony with black, yellow, or variously colored plumes, moss, or “bouquet-like” figures.

Numerous other localities in Presidio and Brewster counties have produced good agate.

Various amounts of agate, jasper, and chalcedony occur in the gravels of the Rio Grande in varying quantities from Big Bend National Park downstream to Brownsville. This agate is found both in the present river gravels and in the older river gravels that now are located on nearby hills and slopes up to several miles north or south of the present Rio Grande. The greatest concentration of agate and related gem materials seems to be in the area between Laredo and Rio Grande City. Vast quantities of excellent gem material have been removed from this area for many years (Pl. IV). The agate occurs as rounded, stream-worn cobbles and commonly has a thin white coating that makes it difficult to distinguish from the abundant chert and other rocks. The agate occurs in cobbles that are mostly 3 to 6 inches in diameter, but specimens of gem quality that exceed twice this size are known. The agate varies greatly in design and color. Plume, moss, banded, and sagenitic agate occur in these gravels in a wide variety of colors. The jasper in the Rio Grande gravels is yellow, red, green, or various shades of these and is commonly suspended as angular fragments in clear chalcedony.

Good agate has also been found near Balmorhea in Reeves and Jeff Davis counties and in smaller amounts at numerous other west and south Texas localities.

Agatized wood (see Fossil wood, pp. 20-21).

Carnelian (translucent reddish chalcedony).—This variety of chalcedony in small quantities has been reported from near Van Horn, Hudspeth County. Small pieces of carnelian have been found in the gravels of the Rio Grande, but finds have been few and scattered.