G&G Features in a Flash: Texas Topaz
May 1, 2024
What is Topaz?
Topaz is a gem valued for its clarity and hardness (Mohs 8) as well as its wide variety of colors, including colorless, yellow, blue, brown, pink, orange, and red.
In its purest state, topaz is colorless, but defects and impurities in the crystal can create color centers. Chromium can cause topaz to turn pink to violet. A combination of oxygen and radiation can turn pink to violet topaz orange, making it the valued Imperial topaz. Other oxygen-related defects can produce brown or blue topaz.
Artificial irradiation and heat treatments can also turn colorless topaz blue. This treatment was first used in 1957 and became widely used during the late 1970s. The low cost and popularity of blue topaz made it the most commonly irradiated gemstone on the market. This treatment is now so widespread that any blue topaz on the market is assumed to have been irradiated unless stated otherwise. Naturally blue topaz is rare and highly desirable.
"Texas Topaz"
Mason County, Texas, is well known in the gem world for producing beautiful topaz. While most topazes found here are colorless, light blue, or brown, some are a natural saturated blue color. These saturated blue stones are known as “Texas topaz” in the trade and are highly sought after for their provenance and natural blue color.
Topaz was first found in Mason County in the late 1800s, long before topaz treatments were developed. For a while, it was considered a local gem. Most gems found were between one to ten carats in size, with the largest ever found weighing 6,800 carats. During World War II, many scientists moved to the Southwest for the nuclear weapons program and began mining recreationally on weekends. This launched several gem and mineral groups in the area and an increased interest in topaz. Topaz from Mason County became popular at faceting competitions and Texas gem and mineral shows. In 1969, “Texas topaz”—blue topaz from Mason County—was recognized as the official state stone.
Texas topaz was still largely a hobbyist’s stone, however, until the early 2000s when Diane Eames and Brad Hodges, owners of a jewelry store in the town of Mason, built a successful jewelry business that focused on locally mined and cut Texas topaz. They launched an advertising campaign that helped this stone reach a national audience and elevated its prestige.
GIA Research on Texas Topaz
Because of its origin, Texas topaz has a much higher regional value than similarly colored topaz from other localities. The two greatest determiners of Texas topaz’s value are the saturation of its blue color and its cut quality. A popular cut style for this gemstone is the Lone Star cut, which produces a five-pointed star shape in the middle of the gem and gives the gem a deep pavilion to intensify its color.
GIA researchers discovered that the most significant trace elements in topaz from Texas were scandium, titanium, germanium, and chromium. GIA researchers used machine learning to predict which stones were most likely from Texas based on their trace element profiles. Machine learning incorrectly classified 7% of the topaz from other countries as being from Texas. Samples from Namibia, Nigeria, Australia, and from California and Indiana in the United States were the most common false positives.
Samples from Brazil, Guyana, Colombia, Zimbabwe, and Mexico had the lowest false positives. GIA scientists were able to study more stones from Brazil, Guyana, Colombia, Zimbabwe, and Mexico than from Namibia, Nigeria, Australia, California, and Indiana. They concluded that false positives were more likely to occur for stones that were not as well represented in their sample (there were fewer of them compared to stones form other locales). It is also possible that topazes from Texas, other U.S. locales, and Australia formed in similar geological conditions, resulting in similar trace element compositions and higher false positives.
Conclusion
Currently, GIA researchers can provide a fairly reliable estimate of the likelihood that a stone originates from Texas. More research needs to be done on larger sample sizes of topazes for country of origin to be determined, however. Nonetheless, these findings suggest that the trace element compositions of most Texas topaz are distinct enough to distinguish them from topaz found in other parts of the world. This implies that determining the geographical origin may become possible in the future, with additional factors such as fluorescence color and inclusions contributing to increased certainty.
Phoebe Shang, a senior writer at GIA, is a Graduate Gemologist.
