Thomas Range "Topaz Mountain"

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Thomas Range (Topaz Mountain)

The Thomas Range is one of the truly classic mineral collecting locations in the world. It has long been known for the interesting occurrence of topaz crystals lining the cavities and vugs in the Topaz Mountain rhyolite. Their brilliant luster, complex crystalline form, and appealing beauty make these crystals desirable to all who are interested in gems and minerals. First visited by Henry Englemann in 1859, Topaz Mountain has been, and still is visited yearly by thousands of collectors seeking topaz and the other rare associated minerals found there.

Location: The Thomas Range is located in the west desert area of Utah approximately 40 miles NW of Delta Utah, in Juab county. Thomas Range Map

Age and composition: The Thomas Range is composed mainly of a series of five or more highly siliceous volcanic lava flows, known as rhyolite, that erupted 6-8 million years ago. The rhyolite, for the most part, is light gray in color and forms a series of dome-like structures. The rhyolite itself is not very uniform in hardness due to substantial amounts of late stage volcanic gases that differentially altered the rhyolite shortly after eruption. This variation in hardness causes the rock to weather with a ‘honeycomb’ like pattern that in some ways reminds one of Swiss cheese. It is within these hollowed out cavities that the minerals of interest occur.

The rhyolites that make up most of the Thomas Range are known as topaz rhyolites. The name topaz rhyolite is given to rhyolitic rocks that are rich in late stage pneumatolitic components that are enriched in fluorine which then form topaz. The composition of the rhyolites of the Thomas Range are the extruded equivalents of a granite pegmatite.

Minerals of the Thomas Range: The following are a list of the minerals that have so far been identified in the Thomas Range:

Important:

Less important:

Collecting locations: While most of the minerals that are found here occur over a widespread area, there are only a few areas within the Thomas range where they occur in sufficient quantity to be of any importance to the collector.

Topaz Mountain Rockhound Area

The topaz mountain Rockhound area (also known as the topaz mountain amphitheater or simply the ‘cove’) is the most important collecting area that is open to the general public. All of the major minerals (with the exception of durangite and cassiterite) can be collected here. It is located in the extreme south eastern end of topaz mountain, which is the southern most mountain within the Thomas Range. Thomas Range Map pictures

Maynard Topaz Mine

The Maynard topaz mine, or simply Maynards, is probably the most important of the mineral locations within the Thomas Range. This location was first visited by Maynard Bixby in the 1890s. It was Maynard Bixby who first collected and described the minerals bixbyite and red beryl (bixbite) at this site, which were subsequently named in his honor. This fabulous location was next visited in 1934 and 1935 by Arthur Montgomery and Ed Over Jr. For the better part of two collecting seasons these historic collectors collected topaz, bixbyites, and many of the other unique specimens found there. They found excellent specimens of bixbyite and a few decent topaz specimens, however, the true ‘treasure’ at this locality still remained undiscovered. Between 1935 and 1973 the locality was visited by a very few collectors who found the usual bixbyite specimens and a few gooD topaz crystals; still the Maynard treasure remained hidden. The area was next visited by John Holfert in the spring of 1973 (at the time John was doing his masters thesis on the minerals of the Thomas Range). The following is a description of the fateful day when ‘Maynards treasure’ was discovered, quite by accident:

“It was a rather hot day in late April of 1973 when I was doing some mineral sampling on a hill side, away from the ‘main’ collecting area. I was trying to determine the extent to which bixbyite and the other minerals occurred within the general area. By early afternoon nothing very remarkable turned up and I was rather discouraged.. Being as hot as it was, I decided to relax for a few minutes under the shade of a large brushy bush that managed to take root along the barren hillside. When it was time to get back to work, I leaned down and propped myself up with my screwdriver that I held in my right hand (a screwdriver is the main tool I use for probing the cracks and crevices). To my amazement, the screwdriver sank into the ground all the way down to the handle. I then pulled out a section of the bush and there, stuck to the roots, were two rather large, perfectly flawless topaz crystals. Thus began the most exciting mineral collecting adventures of my life. It turned out that the bush had grown in to a large gas vent that had managed to break through the rhyolite and reach the surface. Over the next ten years we mined this area and have found spectacular specimens of topaz, bixbyite, garnet pseudomorphs and various combinations of two or more species. Magnificent clusters of topaz; the finest crystallized topaz specimens from the Thomas Range (or the world).”

Maynards is renown for the spectacular clusters of topaz that have been collected here over the years. Calling this location the Maynard topaz mine is a fitting honor for one of the worlds great field collectors. To see maynards from the collectors point of view click on Maynard Adventure.



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