Topaz Mtn., Utah 2005

Over the years, I led several tours from the Natural History Museum at the University of Utah to Topaz Mountain, Utah. My last tour was in 2005. Topaz Mountain is probably Utah’s most famous gemstone collecting site, boasting topaz crystals of color and clarity that rival any to be found anywhere.

General map to the location of Topaz Mountain; (map taken from “A Field Guide to Topaz and Associated Minerals of the Thomas Range, Utah Holfert” 1996)

Topaz Mountain is the southernmost mountain in the Thomas Range. It is light gray to white in color , and it looms conspicuously, being visible from many kilometers. At the extreme southeastern end is a high canyon that has become known as the Topaz Mountain Amphitheater, also sometimes referred to as Topaz Valley, or more simply, “The Cove”. It is approximately 60 km northwest of Delta, Utah, in Juab County. The cove can best be reached, coming from the north, by paved road that starts on State Road 174, approximately 16 km northeast of Delta and pass by the enormous Intermountain Power Plant. “The Cove” has been set aside, by the BLM, as an official rockhounding area, open year-round for collecting with had tools only, and it is the most prolific collecting area open to the general public for free. Topaz Mountain has been, and still is, visited annually by thousands of eager collectors seeking topaz and the other rare associated minerals that are found here. [There is no water or pit toilets available at the site].

The Topaz Mountain turnoff sign from SR 174

The Thomas Range of Utah is one of the truly classic mineral collecting locations in the world. It has long been known for the topaz crystals lining the cavities and vugs of the Topaz Mountain rhyolite. Their brilliant luster, crystalline form, and appealing beauty make these crystals desirable to all who are interested in gems and minerals.

Your typical topaz crystal found within its natural setting at Topaz Mountain.

Pictured above, the topaz crystals are elongated prisms (Orthorhombic), and terminated, may form clusters or even occasionally doubly-terminated crystals. Three types occur within the Thomas Range: transparent, rough opaque and smooth opaque. Most crystals are 1.6 cm or less in length; The crystals vary from water clear to rich sherry amber to light pink; (After being exposed to direct sunlight for a week, the crystals change from the rich sherry color to a light pink and eventually to a clear silver-white color). [They can be reset to the sherry amber if they are held together with radioactivity from Uranium].

Looking west into “The Cove” at the “West Wall” Topaz Mountain, Utah in 2005.

At the location shown above, is where the opaque topaz clusters occur that are very unlike the rough-opaque clusters. They form perfectly smooth, well terminated crystal, that in all aspects resemble the transparent type, except that they are full of small microscopic quartz crystals, giving them a sandy appearance. Sometime these are found partially grown into an open void forming a combination of transparent and opaque topaz. The best chance for collecting topaz for gemstones would be from this area, (up to 8 carats).

Some of my participants collecting topaz at Topaz Mountain within the Thomas Range in 2005

Pictured above, the basic tools that I provided for a tour participant is a 3/16 inch screwdriver, a screen (1/4 inch metal mesh), a 3 pound hammer, a 12 pound sledge hammer, a 3/4 inch chisel, a pry bar, a small army trenching shovel, and a plastic 5 gallon bucket.

Some of my participants collecting topaz at Topaz Mountain within the Thomas Range in 2005

Pictured above, “The White Knoll” is a very altered area. Watch for areas that show increased alteration. Areas that are very light colored (almost white) or areas that have a sugary texture may be mineralized with topaz. Areas that show brown stains along small fractures or seams usually indicate the presents of weathered hematite, which is usually indicative of mineralized areas. A topaz bearing gas vent is one of the key mineralogical features found at Topaz Mountain since it may contain several dozen or more crystals.

Some of my participants collecting topaz at Topaz Mountain in 2005

Pictured above, into “White Canyon”, my participants are looking for opening in the rock. Mineral bearing pockets or seams may appear as nothing more than a thin line on a rock on the surface; these type of features should always be probed with a screwdriver to test for soft spots or openings. Large cavities may contain plugs separating the various crystal chambers. A “plug” is a frothy chunk of rhyolite found within a cavity or fracture that has been completely altered on all surfaces by volcanic gases. Topaz often crystallize on these plugs.

Looking north at “The White Knoll” at Topaz Mountain within the Thomas Range in 2005.

Pictured above, the Thomas Range is composed mainly of a series of five or more highly siliceous volcanic lava flows, know as rhyolite, that formed 6-8 million years ago. The Topaz Mountain rhyolite is not uniform in hardness due to substantial late stage volcanic gases that differentially altered it shortly after eruption. This variation in hardness causes the rock to weather in a honeycomb pattern. It is within these hollow out cavities that the unique and beautiful topaz occur. The Thomas Range rhyolites are the extruded equivalents of a granite pegmatite, but shallower to the surface that allows gases to expand.

A public domain USGS map of the Thomas Range

Pictured above, the rhyolite that formed Topaz Mountain is the youngest of the five volcanic flows. It varies from a light gray (almost white) to a reddish brown. In some areas the rhyolite is had and devoid of any cavities or other structures (particularly the darker red colored rock) while in other zones the rock is highly altered to a lighter and much softer, cavity rich rock. It is within these cavity rich zones that the better specimens are found.

My tour participants posing at the shaft head of the Bell Hill Mine (a Beryllium Mine) within Spor Mountain of the Thomas Range 2005.

Pictured below, west of Topaz Mountain on SR 174 for another 15 km, it forks when it enters the Spor Mountain Mining District. Flourspar and uranium mines are located to the north and the beryllium mines are located directly to the west at the fork. Pictured above is the Bell Hill Mine with Brush Wellman Mine dumps nearby.

Map of the Spor Mountain Mining District; (image taken from “The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western U.S., Christiansen, Sheridan & Burt SP 205; 1986)

From 1944 to 1980, the district yielded 350,000 tons of fluorspar ore from mostly the Lost Sheep Mine (pictured below). Uranium production here from 1948 to 1970 was approximately 105,000 tons of uranium ore, and over 95% from the Yellow Chief Mine. Beryllium ore production from 1970 to the 2020 was approximately 3 million tons. This Beryllium mine is the largest producer of Beryllium in the World.

My tour participants, exploring the Flourine Queen Mine within the Spor Mining District of the Thomas Range 2005.

Pictured above, Spor Mountain consists of a southwest-tilted block of Ordovician to Devonian carbonate rocks and some interbedded shale and orthoquartzite on the northwest flank of the late Eocene Thomas caldera. These sedimentary strata are unconformably overlain by Eocene to Miocene volcanic and volcaniclastic rocks. All of the Be deposits in the district are associated with the 21 million year old, high-silica, topaz rhyolites of the Spor Mountain Formation. The Spor Mountain Formation is in turn overlain by the post-mineral, 6 million year old Topaz Mountain Rhyolite.

Geological map of Fumarole Butte; (map taken from the public domain source of the United State Geological Service).

Imaged above, is a geological map of Fumarole Butte, 15 km east of Topaz Mountain. Fumarole Butte is a shield volcano that erupted during the Quarternary period (one million years ago) and is composed of basaltic andesite. It stands 207 meters in height and has a diameter of 12 kilometers. Under the volcano lies Crater Bench, the result of an eruption of basaltic andesite. To the east of the volcano are a series of hot springs, known as Crater, Baker Hot-springs, or Abraham Hot Springs.

Some of my tour participants enjoying the water at Baker Hot-Springs in 2005.

Pictured above, at Baker Hot-Springs, the hot mineral water emerges from the spring at 180 °F/82 °C. The primary mineral is manganese and has a high sulphur content giving it the characteristic “rotten egg” smell. The spring water discharges at 17 gallons per second, and flows into three concrete soaking pools, approximately 5′ x 8′; these concrete structures are all that is left of an old resort. Next to the soaking pools is a channel with cold spring water that can be diverted into the soaking pools to cool the water. As mentioned above, the hot springs and seeps are located on Fumarole Butte which is a basaltic andesite type of shield volcano from the Quaternary period, overlaying basalt and rhyolite.

Map of Little Sahara Recreation Area; (image taken from the public domain site of the Utah State Park Service).

Imaged above is the Little Sahara Recreation Map, just 50 km east of Topaz Mountain, on a very well graveled road. The locals call the place Jericho Sand Dunes.

Looking west from Highway 6 at the Little Sahara Dune Field in 2005.

Most of the sand at Little Sahara is the result of deposits left by the Sevier River, which once flowed into ancient Lake Bonneville 15,000 years ago. After the lake receded, the southwesterly winds that flow across the Sevier Desert picked up the exposed sand.

Sand Mountain found at the Little Sahara Recreation Area, (Image is of Public Domain)

Pictured above, Sand Mountain, in the middle of the dune field, deflected the wind upward, causing it to slow and drop its load of sand.

Sand from the Little Sahara Dune Field in Utah 2005.

Pictured above and below, sand particles, composed mostly of quartz, fell downwind among the sagebrush and juniper around Sand Mountain, ultimately creating a 124 square-mile system of giant, free-moving sand dunes.

Looking west from Highway 6, towards Sand Mountain and the Little Sahara Recreational Area in 2005, (Jericho).

Little Sahara Recreation Area is 60,000 acres of sagebrush flats, juniper-covered hills, and free moving sand dunes located in Juab County, Utah. and east of the Thomas Range and Topaz Mountain.

The Jericho Sand Dunes in West-Central Utah.
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