The Gemstones of Texas
The state of Texas lies on mainly sedimentary rocks where former coastlines spanned the region during the rising and falling of sea levels in past geologic ages. This type of structure does not give rise to many of the better known varieties of gemstone but, as any native will tell you, Texas is big. Covering a region of nearly 270,000 square miles, second only to Alaska in size, the State has some fascinating gemmolocical surprises in store.
A number of books mention diamond finds in Texas, indeed there is a Texas diamond on display in the Smithsonian collection. Only a handful of stones of any significant size have ever been discovered and the last authenticated finds were made early in the last century. Such diamonds were probably transported by erosion from far-off primary sources many ages ago and the likelihood of any more turning up is negligible. Pearls have also been reported because natural freshwater pearls were once common throughout Continental North America, particularly in the Mississippi Basin. Changes to the use of waterways, pollution and overfishing has put paid to most of them although they occasionally turn up in old collections. So without diamonds, pearls, rubies, sapphires or emeralds, what are the treasures of Texas and what makes them so special?
In the very centre of the state there is a region of very ancient, very hard rocks similar to those of the Appalachians. This is the Llano uplift and it brought with it the natural blue topaz, State Gemstone of Texas. Topaz is hard and resists erosion so these gemstones are to be found on the surface of the collecting sites, sometimes with a worn, frosted appearance that makes them difficult to distinguish from quartz. For those who are more familiar with the brilliant, kingfisher blues of Brazilian irradiated topaz, the gentle range of colours from sky blue to ice white will be a surprise. The price of genuine Texas topaz can also be something of a surprise but anyone who has spent days or even weeks prospecting in order to come home with nothing more than sunburn and backache will readily understand. A unique ornamental rock, llanite, is quarried nearby. It is a complex rhyolite containing reddish feldspars and lovely little spangles of blue quartz. Llanite has been fashioned into cabochon gemstones, spheres, carvings and paperweights, it is prized for its beauty, its even texture and the fact it is unique to Texas.
The Western Counties of Texas contain a series of complex geological faults giving rise to the State's highest elevations, some spectacular landscapes and an incredible variety of agate species. Rock hounds travel to West Texas from all over the country to hunt for these exquisitely plumed and banded agates. Having such distinct colouring and internal characteristics, they are usually named after individual towns or ranches such as Terlingua and Balmorhea or Woodward and Bishop but occasionally a descriptive name such as the delightful “Christmas agate” is used. Also to be found are petrified wood, fossil coral and dinosaur bone although not in the same quantities as in the States further to the West. The Pecos River is shared with New Mexico and so are the erroneously named “Pecos diamonds”. These are broken, water worn crystals of quartz which are really anything but gemstones. They do, however, have some interesting shapes and dedicated hunters may be rewarded with a few stones of the attractive tangerine variety. Amethyst has been reported in Western Texas but, with the exception of a few slightly purple crystals inside the occasional agate, fine Texan amethyst is the the stuff of legends.
The sedimentary rocks of the Texas Panhandle are known the world over for the production of oil and gas without containing other geological treasures to rival the discovery of “black gold” but a unique variety of flint known as Alibates is found on the surface near the recreational Lake Meredith. It occurs in pretty shades of pink and blue and was once highly prized by Native Americans for its knapping properties. It has become very desirable in recent years as these tool making techniques are being rediscovered and it also makes attractive cabochons. Otherwise the region yields only a few agates from the Canadian River and some good quality petrified wood.
The Eastern and Coastal Counties of Texas have much in common geologically with Louisiana, Mississippi and Continental Florida. Vast forests of fast growing ferns covered these warm, wet regions for long periods and much of this vegetation has been petrified in such a way as to show the finest botanical detail when the specimens are sliced and polished. Petrified fern wood is the Texas State Rock and, when the parallel tubes which run through its structure have been captured in contrasting colours, it makes a handsome cabochon. Particularly sought after are the slices which have a cream exterior and a black heart. This is one of those areas where the labeling of specimens is extremely important as even a paleobotanist would be unable to decide which side of the State border one of these specimens came from once its provenance was lost.
Similar geological conditions continued down the coast to the Southern Counties of Texas although the region has not much appeal to rock hounds, possibly because there is nothing there to compare with the gemstone treasure trove to be found South of the Mexican Border. Pebbles of plume and banded agates have traveled the whole length of the Rio Grande and are sometimes to be found on its shores, the best known in the region being Laredo agates. These stones have an unpromising exterior but the red, yellow or green jasp-agate found inside takes a fine polish. Petrified wood is also to be found and, while there is nothing hereabouts to compete with the wonderful gemstones of Western Texas, someone from way down South looking for their own particular gemstone would not be disappointed.
Nearly all Texan collecting sites are on private land and the relevant permissions must be sought, to say nothing of taking appropriate safety precautions. Also, collecting of any sort is strictly forbidden in National Parks. However, the rock hounding hobby is not dead and people still go hunting for gemstones no matter how loudly the old timers complain that there is nothing to be found out there any more. It can still be a very enjoyable activity but good finds on the ground are few and far between. A day in the fresh air is sometimes best rounded out with a visit to one of the remaining local rock shops where lovely specimens can be bought. When pieces from old collections come up for sale they are worth snapping up in spite of the fact that they are unlikely to be cheap, in addition some specialist dealers may be able to find what the amateur cannot. Genuine Texas gemstones may cost more than the equivalent type of stones from other parts of the world but they cost nothing like as much as diamonds. On the other hand, they are often rarer than diamonds, extra special to both the giver and the receiver and endowed with that essential Texan attribute – a really good story.
Nicola Ainsworth B.Sc. F.G.A.
27th June 2008