Texas is a huge state with incredibly diverse geographical features, from sandy beaches and lush hill country to dry, scrubby desert. In all of Texas there are a wide range of gems and minerals and fossils. Remember that there are almost no public lands in Texas, so permission for gems to be excavated on private lands is necessary. Some digging sites require you to pay a day’s cost for digging different gems and minerals.
Where are Rare Gems & Minerals found in Texas?
Rich brown to yellowish amber has been found near Eagle Pass, Maverick County, in Cretaceous coal and on Terlingua Creek, Brewster County. Although much of this material is translucent and the quality suitable for lapidary purposes, the pieces are seldom more than a fraction of an inch in diameter.
Occasional finds of poor quality brownish amber have been reported from the
Tertiary formations of the Gulf Coastal Plain, but thus far no gem quality material has been found.
The softness of amber limits its use to brooches, necklaces,and other jewelry that is relatively safe from abrasion.
Augite of gem quality occurs near Eagle Flat, Hudspeth County, Texas. Although this material is very dark greenish brown and not commonly thought of as a gemstone, lapidaries have used it to fashion black faceted stones and cabochons that resemble obsidian. Most of the augite occurs as loose pieces and crystal fragments that have weathered out of nearby igneous rocks; the augite can also be found in situ in the igneous rocks.
Specimen sand pieces of cutting quality 1 inch in diameter are common, and fragments over 2 inches in diameter have been found. The augite is associated with black spinel and some dark gray to black pieces of natural glass. Although the faceted and cabochon-cut stones are not particularly attractive, some of the larger pieces of augite might be utilized for carving.
Beryl crystals have been found in pegmatite dikes in Llano, Blanco, and Gillespie counties. These crystals are commonly several inches long and exceed 1 inch in diameter but are very badly fractured. Most of the beryl crystals do not approach gem quality and are entirely unsuitable for any lapidary use. The color of the crystals found thus far is bluish,greenish, pinkish brown, yellowish, and colorless. Some very tiny colorless beryl crystals have been found that are transparent,but thus far such crystals have been too small to be cut into gems.
Fine blue beryl crystals have been found in the Franklin Mountains near El Paso, Texas. Unfortunately, these crystals are so badly flawed and fractured that they are not suitable for lapidary use.
It seems likely that careful prospecting of Texas pegmatites will reveal at least some gem-quality beryl.
Celestite is very seldom cut into gems. Being very soft, brittle, and having three cleavages, celestite is completely unsuitable for jewelry. These same properties make this mineral exceedingly difficult to facet; however, faceted stones are seen in large collections.
Fine crystals of colorless and blue gem quality celestite have been found at Mount Bonnell and other localities west of Austin, Travis County. The celestite crystals occur in vugs or geodes in limestone. The crystals are mostly white or colorless and fractured near the base or where attached, but the tips of the crystals are commonly clear celestine blue and completely free of flaws.
Crystals several inches in length have been found, but the average size is about 1 inch. The smaller crystals are frequently more transparent and consequently better suited for cutting. It is very difficult to obtain crystals that will allow the cutting of flaw less stones of more than 4 or 5 carats.
Bluish and colorless celestite of gem quality and fine crystals have been found near Lampasas, Lampasas County, and near Brown wood, Brown County, but neither of these localities has been very productive of good gem material.
Celestite geodes have been found in parts of Coke, Fisher,and Nolan counties, but these geodes contain little gem material.
There is only one well-authenticated find of diamond in Texas. A small brownish diamond was found in1911on section 64, block 44, Foard County. The exact weight of the stone has not been recorded, but one authority estimated that it was of sufficient size and clarity to yield a cut stone of about one-quarter carat.
The only diamond-bearing rocks known in the United States are in Pike County, Arkansas. Although many other diamonds have been found in the United States, all were loose in gravels or streams except for some stones at the Arkansas locality. The fact that one diamond was found in Foard County does not mean that the prospects of finding more diamonds in Texas are much better there than anywhere else in the State. It is highly unlikely that more than a very few diamonds will ever be found in Texas, and any stones that may be found in the future are likely to be widely scattered.
Llano County has furnished some green and brownish-green epidote that is suitable for cutting into cabochons. Most of the material that approaches gem quality has come from contact metamorphic zones and is associated with garnet,quartz,and some scheelite. Some small cavities in the rocks contain tiny transparent crystals of gem quality, but the largest obtainable flaw less faceted stones would probably be less than 15 points.
Faceted stones of epidote are sometimes known as pistacite owing to their common pistachio-green color.
Very fine green, transparent fluorite has been found near Voca, Mason County.The fluorite occurs as vug fillings in pegmatites, associated with crystals of pink microcline and colorless quartz. Most of the vugs have been completely filled by the fluorite; therefore, crystals of the fluorite are not too common. Masses of fluorite several pounds in weight, rich green, and quite transparent have been found near Voca. Transparent pieces an inch or more in diameter are common.
Fluorite is much too soft for everyday use in jewelry and because of the low refractive index does not yield brilliant faceted stones. The perfect four-directional cleavage, relative softness, and brittle tenacity of the mineral make it difficult to facet. Faceted stones are seldom seen outrside of collections. Cabochons are also difficult to cut from this material, but the rich color obtained is ample reward for the time and care necessary in cutting.
Fluorite occurs at several other localities in Texas, notably in Hudspeth, Brewster, Presidio, Llano, and Burnet counties, but not commonly in gem quality or colors that warrant its use as gem material.
Gadolinite as a cut gemis not seen outside of large collections; however, it can be faceted into black opaque stones of little beauty but of great interest to collectors. The best known locality of this mineral in the United States is Baringer Hill,Llano County, Texas. Unfortunately, this locality was completely flooded by the completion of Buchanan Dam in 1938. Masses and rough crystals of gadolinite weighing over 100 pounds were mined from this locality.
The gadolinite occurred in a large, very coarse-grained pegmatite dike associated with quartz, microcline, and fluorite, as well as allanite, fergusonite, nivenite, cyrtolite, thorogummite, and various other rare minerals. Some of the minerals in the dike occurred in very large masses. One quartz mass over 40 feet in diameter was noted,and microcline masses up to 30 feet in diameter were not uncommon. Much of the gadolinite was used by industrial firms as a source of thorium compounds, although some specimen and gem material found its way into museums and private collections. Because the locality was worked mostly from 1910 to about 1925 and because since 1938 the waters of Lake Buchanan have completely flooded the entire area, material from this locality is now exceedingly difficult to obtain. The collection of the Smithsonian Institution, Washington, D.C., contains a cut and polished gem of Baringer Hill gadolinite that weighs 8.6 carats.
The garnet group of minerals is variable in composition. Listed below are the pure members of this group, but garnets found in nature are usually a mixture of two or more of these end members.
Good crystals of gem-quality almandite garnet have been found in Llano, Blanco, Burnet, and Gillespie counties. In southeast Llano County, northwest Blanco County, and northeast Gillespie County, the stones mostly occur in stream gravels where they have collected after being weathered out of compact mica schists.
Owing to the fact that most of the garnets have not been transported very far from their source, the stones commonly show good crystal form. All of the garnets from one locality commonly do not have exactly the same crystal form. The garnets are mostly widely scattered in the stream gravels but can be found concentrated behind rocks and on small gravel bars.
Many of the crystals are less than one eighth inch in diameter; however, good crystals one-fourth to one-half inch in diameter are common.Most of the stones are too fractured or have too many inclusions to yield gems,but many transparent stones have been found. The transparent crystals usually yield flawless deep red faceted stones of 2 carats or less. Some of the stones that contain too many inclusions to facet are cut as cabochons and are then often known as carbuncle.
Small garnet fragments have been found in streams and in gneisses and pegmatites near Castell, Llano County, but they are not commonly of gem quality.
Occasional small gem-quality garnets have been found in pegmatites and contact metamorphic zones in Burnet County. Garnets have also been found in several other counties, notably Mason, El Paso, Hudspeth, and Culberson, but no stones of facet quality have been reported.
Very fine facet-quality labradorite has been found about 20 miles south of Alpine, Brewster County. The labradorite occurs loose in the soil as slightly weathered or frosted cleavage fragments, commonly showing one or more crystal faces. The pale-yellow or straw-yellow color of these fragments, as well as their lack of internal imperfections, makes these stones excellent gem material. Individual pieces that exceed three-fourths inch in their longest dimensions are rare. Cut stones of more than 5 or 6 carats from this locality are scarce. The source of this material is uncertain, but it is probably weathering out of an underlying igneous rock.
Very fine crystals of blue microcline have been found east of Packsaddle Mountain and near Kings land in Llano County. Crystals exceeding 1foot in length have been found,although most are only a few inches long. The color of the microcline is mostly pale blue, but some crystals are darker. Microcline crystals associated with milky or vein quartz, smoky quartz, some biotite, and rarely cassiterite occur in pegmatite dikes which vary in size from a few inches to several feet in thickness.
The color of this microcline is pale in comparison to microcline from someother localities in the United States, but the Texas blue microcline does yield pleasing cabochons. Perfect crystals of this material are prized by collectors. Blue or greenish microcline is often called amazonite or amazon stone.
Bluish microcline associated with quartz and topaz has also been reported near Katemcy, Mason County.
Red microcline is common in several central Texas counties and is a primary constituent of many of the igneous rocks in those counties. Large crystals of perthitic red microcline occur in pegmatite dikes of Mason,Llano, Burnet,and Gillespie counties. Any feldspar quarry or other pegmatite mining operation in anyof these counties is likely to containlarge red microcline crystals and fragments. Unfortunately, the good crystals that may have been present are often shattered by blasting during quarrying operations.
Gem-quality black and dark-gray obsidian has been found in Presidio County associated with extrusive igneous rocks. The obsidian in this area is too opaque to serve as attractive faceted stones but is found in pieces of sufficient size and quality to yield nice cabochons. Some of the small weathered pieces of this material resemble tektite in out ward appearance; in fact, the “valverdites” mistaken originally for tektites are pebbles of weathered obsidian in terrace gravel of Val Verde County. Obsidian takes a high polish but is very sensitive to heat. Stones that are slightly over heated during grinding or sanding will quickly shatter. Obsidian of gem quality has been reported also in Brewster County.
Opal other than as fossil or opalized wood occurs at the following several localities in Texas. Approximately 16 miles southof Alpine, Brewster County, precious opal occurs in very small seams and as cavity fillings in very hard pinkish-brown rhyolite. This opal is milky or bluish and commonly exhibits small flashes of blue, green,red, and orange fire. Individual pieces of this opal are mostly quite small, rarely over one fourth inch in diameter, and very difficult to remove from the tough rhyolite matrix.
Pearls are the result of the secretion of calcium carbonate by various shellfish around sand grains, parasitic organisms, shell fragments, or other foreign objects that have in some way entered the body cavity of the shellfish. Since the shellfish is unable to expel these irritating particles or organisms, it deposits successive layers of calcium carbonate around the foreign substance to make it smoother and less irritating. Although pearls are principally calcium carbonate, they also contain small amounts of an organic substance, called conchiolin,and water.Pearls are found in shellfish that live in either fresh or salt water
The quartz family gemstones can be divided into two groups for purposes of description. The first group is the crystalline varieties,or those quartz varieties that commonly occur in distinct crystals. The second group is the cryptocrystalline varieties, or those quartz varieties that occur as irregular masses that are composed of many microscopic crystals. The crystalline varieties are usually much more transparent and are most often seen as faceted stones. The cryptocrystalline varieties vary from sub-transparent to opaque and are almost always cut as cabochrons.
In central Texas, in the Llano River area, particularly near the city of Mason and in the hills of Mason County, many exceptional specimens of blue topaz are found.
The few areas where blue topaz takes place in Texas are private, but you can check for topace specimens for a small cost at several fee digging locations. The Lindsay Ranch, Seaquist Ranch and Bar M Ranch are among the most famous locations.
Topaz screens are usually available at prices between $15 and $25 a day.
The colorless crystals and light-blue shades of topaz are found. Most crystals are small, but over the years some of the better sites have recovered big, quality pieces.
The Amethyst Mountains are known to have a deposit of the crystal however the amount or quality of the amethyst found there has not been recorded. The name of the mountain was suggested by the Geological department of the United States after an expedition to its summit as amethyst was found there.
Two forms of chalcedony or cryptocrystalline formations are agate and jasper. In Brewster County, near the western town of Alpine, is available Moss agate that looks like a blue cheese, red and black agate. In the western central county of San Saba, in San McCulloch, and the north panhandle of the Moore County jasper, the shape of the jasper is typically red, green, yellow or gray.
Texas Gemstones By Elbert A.King, Jr., The University of Texas at Austin, Austin,Texas.