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.

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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.

 

LOWER COLORADO RIVER TRENCH

PARKER DAM WAS BUILT AT A NARROW POINT IN THE VOLCANIC ROCKS

COLORADO RIVER TRENCH AT PARKER STRIP

 Most people in Colorado are probably unaware that the Arizona-California border is the Colorado River where numerous dams back up large lakes.  Arizonians refer to the area as the West Coast.  Starting  near Las Vegas with Lake Mead and Hoover Dam, the river has cut several deep canyons on the way south to Yuma, AZ and ultimately to its delta in the Gulf of California.  At times in the recent past the river actually emptied into the Salton Sea to the west of the current trench, an area created by faulting associated with the San Andreas Fault.  Now the river does not actually reach the Gulf as water is diverted off for irrigation and culinary use, evaporation rates are high, and the delta has blocked the channel.

Lake Mohave, about 65 miles in length, is downstream from Hoover Dam and behind Davis Dam. Parker Dam backs up Lake Havasu for 45 miles and is the source for both southern California drinking water (Colorado River Aqueduct) and the Phoenix metro area (Central Arizona Project).  Following those dams are the Palo Verde and Imperial dams.

I was amazed that the river near Parker, Arizona, (about midway on the border) is crystal clear and quite deep.  Geologists still are uncertain about the exact age of the lower Colorado River and the formation of the Grand Canyon (you will see figures ranging from 65 Ma to about 5 Ma).  What is known is that the river turns south near Vegas, cuts through mountain ranges, creates some fairly deep canyons, and pretty much runs in a straight line to the Gulf.  The path was at least partially determined by a series of faults and down-dropped basins here in the Basin and Range Physiographic Province.

At one time geologists believed the Gulf of California extended north nearly to Las Vegas and that the Colorado River simply keep cutting and following its retreat to the current location.  The evidence for this was the late Tertiary Bouse Formation, which in its lower reaches contains marine invertebrates.

Jon Spencer and Philip Pearthree of the Arizona Geological Survey have produced a great story of the Colorado River evolution in the Winter 2005 edition of Arizona Geology (http://www.azgs.state.az.us/), and the following summary is from that article:  Geologists now believe that the Bouse Formation was deposited by the Colorado River in a series of lakes that filled with river water and spilled over, eventually linking the river with the Gulf of California.  At the mouth of the Grand Canyon, the Colorado River first arrived less than 6 million years ago. Along the course of the lower Colorado River, it appears that all of the Bouse Formation was deposited between 5.5 and 5.3 million years ago and Colorado River sands arrived in the Salton Trough less than two hundred thousand years after deep flooding of Mohave Valley. The influx of Colorado River water and sediment at this time marks the inception of the modern Colorado River.  The modern Grand Canyon began with spillover of a very large lake in northeastern Arizona and rapid incision of the lake outflow point about 5.5 million years ago.

As for the marine invertebrates, recent studies show that evaporation in the southernmost lake as it was filling with river water (the only location for the fossils) could have elevated the salinity to sea-water levels.  Most likely birds transported the initial organisms to the inland waters.

I have been camped here at Buckskin State Park on the “Parker Strip” for a couple of weeks and have been exploring the geology.  It is complex, especially for a short-time visitor like me.  The rocks range in age from Precambrian crystalline to Paleozoic limestones to huge amounts of Tertiary volcanics to the sedimentary Bouse Formation and other basin-fill sediments to Quaternary gravels.  There are the lower plates rocks and the upper plate rocks and the detachment faults and the normal faults and the thousands of feet of sediments associated with the river that fill all of these paleovalleys along with the overlying terrace deposits.  It is a “jumbled mess” and I certainly appreciate the skill of the mapping geologists.  

mike

THE PINNACLE OF TOURIST SLEAZE--LONDON BRIDGE

VOLCANIC AGGLOMERATE

BASIN FILL SEDIMENTS AND SEDIMENTARY ROCKS

VIEW FROM THE EASY CHAIR

AT SOME LOCALITIES SAND HAS BLOWN FROM THE RIVER BED AND SANDBARS (PRE-DAM DAYS) AND CREATED DUNE FIELDS