Several decades ago, a trip to the Topaz Mountain rockhounding area in the Thomas Range northwest of Delta, Utah, was often the highlight of a mineral collector’s year. Topaz Mountain, true to its name, hosts transparent, champagne-colored topaz [Al2SiO4(F,OH)2] specimens deposited in small cavities in a Miocene-age rhyolite lava dome. These open spaces were once filled with superheated volcanic gases, from which the topaz was deposited, as the gases slowly cooled. Other minerals also present within these cavities include thumbnail and micro-sized crystals of drusy quartz [SiO2], specular hematite [Fe2O3], bixbyite [(Mn,Fe)2O3], pseudobrookite [Fe2TiO5] and red beryl (Be3Al2Si6O18). With a good hand sledge, a couple of sharp chisels and a gadbar, a few hours’ of hard work would usually reward each collector with at least two or three classy topaz crystals a half-inch (12 millimeters) or more in length, often on matrix, and several specimens of the other minerals. These specimens were reasonably easy to collect from outcrop exposures and loose boulders. The Topaz Valley at the south end of the mountain was the favorite collecting area, and also a nice place to camp. Back then, the road in the wash going into the valley used to sparkle with tiny shards of topaz in the soil.
This August (2011), a friend and I made our first visit to Topaz Mountain in a decade, and as Marvin Gaye once sang, “Things ain’t what they used to be.” Years back, early on a day in midsummer, there were enough rockhounds in the valley that parking places near the prized, rocky hill known as The Knob were hard to find. But this August there were more pronghorns than people in the Topaz Valley; we were the only visitors besides several ATV riders. Once we reached The Knob the reason hit us. There was nowhere left to put a chisel into what is now left of the rocky outcrop!
Even the backside of what was once The Knob is now skinned off to smooth, hammered rock. The outcrop walls of the valley, especially the west wall, have also been skinned nearly smooth. The only accessible rocks to break without extensive work with heavy sledges, chisels and large prybars were boulders in the washes. After several hours of boulder-busting, we together found several good and half a dozen fair thumbnail specimens of topaz, and several other fair small matrix pieces. We did not find any of the less-common minerals, but counted ourselves lucky to have found anything at all. Most of the sparkle is even gone from the road – someone has apparently even screened the wash for all but the tiniest shards of topaz.
There is still plenty of topaz deep in the rhyolite of the Thomas Range, but do not expect to find it easily. Plan to work hard and stay late, and take plenty of water. It just might be worth the effort!