BIXBYITE: A MINERAL FOR YOUR COLLECTION; & RED BERYL

RHYOLITE EXPOSED IN THOMAS RANGE

The Thomas Range, and other nearby mountains in the West Desert of Utah, are some of my favorite places to visit and collect and I have made numerous trips to several localities.  I am always fascinated by the relative abundance of topaz crystals but also appreciate some of the less common minerals such as bixbyite. 

Bixbyite is a manganese iron oxide, ( Mn,Fe)₂O_3, named for Maynard Bixby, an early collector and explorer in the Thomas Range (the type locality for the mineral).  Bixby also had a Colorado connection for in 1894 he published A Collector in Colorado.  Bixbyite has a black streak, a metallic luster, a black color, a hardness of around 6-6.5_, and a specific gravity of about 5.  It belongs to the isometric crystal system and generally occurs as small (on the order of 3/8 inch) euhedral cubes that are sometimes striated and sometimes modified (the corners seem “cut off”).  In most cases, the mineral looks like a black cube of pyrite and has a similar streak, hardness and specific gravity.  Bixbyite occurs in the same mineralogical environment in the Thomas Range as does the topaz---in lithophysal cavities of the rhyolite.  In fact, bixbyite often is found “growing with”, and appended to, the topaz crystals (I am certain there is a mineralogical term for this growth).   

Bixbyite cube attached to topaz.  Length of topaz ~ 1.5 cm.

Single cube of bixbyite ~6.5 mm.

Although various mineral databases list several localities where bixbyite may be found, the Thomas Range is the best known locality in the U. S.   I have seen specimens collected from the Marysvale District in Utah but otherwise have not collected from the Arizona localities noted at www.mindat.org.  Eckel and others (1997) did not list a collecting locality in Colorado for bixbyite.  And, specimens seem rare in rock shops other than a those located in Utah.  So, bixbyite seems like a nice specimen mineral for the display case.

Not to be confused with bixbyite is “bixbite”, an early name sometimes still in use for what is now known as red beryl.  “Bixbite” was also named for Maynard Bixby with a type locality in the Thomas Range.  However, the name is no longer recognized as valid and specimens are correctly known as red beryl or beryl var. red, although Red Emerald has come into use as a trade name.  It is a silicate, Be₃Al₂(Si₆O₁₈), belonging to the hexagonal crystal system and usually appears as small elongate or tabular prisms.  Red beryl has a vitreous luster, a hardness of 7.5-8.0, a specific gravity of around 2.7 but exhibits a low dispersion and a low refractive index.  Its red color, the primary reason for its value, has been described as “raspberry red”.  As best that I can determine, the red color is most likely due to manganese and small amounts of iron, chromium, and calcium substituting for some of the Al ions (Ege, 2010).  At any rate, all gem beryls (yellow heliodor, green to blue aquamarine, salmon to pink morganite, very intense green emerald, and the colorless goshenite) are fairly expensive as faceted gems.  However, red beryl is by far the most expensive of the gem beryls and perhaps one of the most expensive gem stones in the world.  As with many gems, the price is often directly related to the availability of the mineral, and to the quality and color of the stone.

 

Red beryl from the Wah Wah Mountains.  A natural stone in the rhyolite and a faceted specimen.  Photo courtesy of Red Emerald.com.

Although red beryl was originally described from the Thomas Range, the specimens from this locality are generally non-gemmy and usually consist of small (1/4 inch or less) flat disks; however, a private claim reportedly has located a few gemmy crystals near Wildhorse Springs.  As with topaz and bixbyite the red beryl occurs in lithophysal cavities in the rhyolite, a situation different from the occurrence of most other beryls found in pegamatites.

As far as I know, all gemmy red beryl comes from a claim in the Wah Wah Mountains south of the Thomas Range where a commercial mine is producing (or has produced--it may be closed), perhaps 22-27 grams of red beryl per ton of ore.  I visited the the Harris Rock Shop in Delta, Utah, and observed several examples of red beryl with some specimens selling for several thousand dollars.  At various rock shows I have seen faceted specimens, 12 or 13 per carat (so very tiny), with a price tag of around $1000.  One .43 carat gem recently sold on a web site for $2150.  In 2005 a faceted 1.79 carat specimen reportedly sold for $15,000; I expect there are more expensive offerings.   In 1967 the Harris Family purchased the red beryl claim for $8000; in 2000 “capital payment reaching $5.5 million and transfer of Title to Leases made by landowners to GMI” was made (author unknown, 2010).  Today rumors on the market whisper about price tags on the order of $10 million for the mines!  I doubt if many other gem mines in the U. S. have created such interest.

Durangite.   Photo courtesy of University of Utah and photographers  John Holfert and Jeff Scovil.

Red beryl in the Wah Wah Mountains of southwestern Utah formed ~20 Ma as a post-magmatic mineral in a topaz rhyolite lava flow, the Blawn Wash Formation.  Unlike topaz (and the red beryl of the Thomas Range), this beryl occurs along fractures in devitrified rhyolite occupying a graben.  Alteration may be related to the incursion of surface water along shrinkage fractures within the flow and the interaction with fluorine-rich gases and beryllium. (Thompson, T.J. and others, 2002).  

One mineral that I have never seen from the Thomas Range on my many trips is durangite, an exceedingly rare sodium aluminum arsenate fluoride (NaAl(AsO₄₎F) known from only a single claimed locality in the Thomas Range.  The few specimens that I have seen in collections are orange-red to red in color with a vitreous luster and a hardness of 5.5.  The mineral is only known from a few localities in the world and the Thomas Range specimens seem the “best”.

Forty plus years ago I collected garnets in the Thomas Range; however, I have not visited the site in 45 years. My sometimes foggy memory does recall collecting some nice, small trapezoidal crystals in Garnet Basin, on the west side of the Range. However, over the years and many personal locality moves, “things” just sort of disappeared---like these garnets.

 

Garnets on a topaz crystal.  Photo courtesy of the University of Utah.

So, if you get the chance, take a trip to the West Desert and pound the rhyolite.

 

REFERENCES CITED  

Author Unknown, 2010.  Red Emerald History; Mine History:  http://www.redemerald.com/history.html#minehistory.

Eckel, E. B. and Others, 1997.  Minerals of Colorado:  Denver Museum of Nature and Science and Fulcrum Publishing.

Ege, C., 2010. What Gemstone is Found in Utah That is Rarer Than Diamond and More Valuable Than Gold?: Utah Geological Survey Notes (online publications), http://geology.utah.gov/surveynotes/gladasked/gladberyl.htm.

 .

Thompson, T. J., Keith, J. D., Christiansen, E. H., and Tingey, D. G., 2002. Topaz Rhyolite Hosted Red Beryl in the Wah Wah Mountains, Utah: A Genetic Model and Mine Update [abst]: Geological Society of America Rocky Mountain Section Abstracts with Program.