Saturday, April 23, 2011

CSMS SILENT AUCTION

LIFE MEMBER CHUCK CHECKS IDENTIFICATION 

The annual CSMS silent auction and bake sale was held on 23 April at the Western Museum of Mining and Industry.  President Roger and Vice President Kay supervised the labeling of specimens and Life Member Chuck served as the chief arbitrator for specimen identification, and as the “money keeper”.  Board members Roni and Sharon filled the tables with attractive specimens.  Yam kept the crowd attentive with his booming voice and preciseness of time keeping.  Specimens ranged from polished spheres to fossil fish to a nice selection of fine minerals obtained from the collections of Dennis Beals and Martin Guth.  Bingham was well represented as it appeared that Marge had brought back half the state of New Mexico to share with purchasers. 

My two major acquisitions were: 1) a stunning collection of large quartz points sprinkled with minute crystals of siderite and calcite collected from the San Vicente Mine in Guanajuato, Mexico; and 2) nice cubes of purple fluorite from the Royal Flush Mine, Bingham, New Mexico.

mike 

GREAT BROWNIES AND TARTS BY DIANA

QUARTZ WITH SIDERITE AND CALCITE

PURPLE CUBES OF FLUORITE

Sunday, April 17, 2011

IT IS NOT AN AGATE!


Many rock and mineral collections contain specimens of “turritella agate”; however, the specimens are neither agates nor do they contain the snail Turritella!  Agates are banded (typical such as Lake Superior types) or included chalcedony (many moss agates).  Although “turritella agates” are siliceous, they are neither banded nor included.  Most specimens of “turritella agates” found “for sale” at rock and mineral stores most likely were collected from southwestern Wyoming in the Green River Basin at a locality termed the Delaney Rim.  The Green River Basin was the site of a large freshwater lake during the Eocene Period of the Tertiary (~34 Ma—60 Ma) termed Lake Gosiute.  Related to Lake Gosiute is Lake Uinta that formed in northwestern Colorado (Piceance Basin) and northeastern Utah (Uinta Basin), and Fossil Lake (Fossil Basin) immediately to the west.  The climate around the lakes during the Eocene was tropical to subtropical and the waters teamed with life.  For example, the famous fossil fish localities near Kemmerer, Wyoming, are located in the Green River Formation exposed in the Fossil Basin.  On the lake shores palm trees grew and flamingos waded in the shallow water.  Among invertebrates, the lakes contained millions of snails now assigned to Elimia tenera.  The snails formally were assigned to the genus Goniobasis. Turritella is a well know marine snail (and also differs in external markings from Goniobasis or Elimia).  However, one should be aware that some popular web sites still note such misinterpretations: “Turritella agate is formed from silicified fossil Turritella shells. Turritella are spiral marine gastropods having elongated, spiral shells composed of many whorls”.   And, most rock and mineral stores still label their specimens as ‘turritella agate”!  For a more complete description of the naming problem I refer the reader to a published paper in Rocks and Minerals (Allmon, 2009).

REFERENCES CITED
Allmon, W. D., 2009, The Natural (and not so Natural) History of “Turritella Agate”: Rocks and Minerals, v.84, no. 2, p. 160-165.

mike 
Image from Wikipedia Commons.

Wednesday, April 6, 2011

UTE VALLEY PARK AND THE LARAMIE FORMATION






Arch in Laramie Formation, Ute Valley Park.



The Colorado Springs area is home to some of the world’s most fascinating geological wonders ranging from Pikes Peak (igneous rocks, mostly granitic, emplaced about 1.1 billion years ago) to majestic ridge- and spire-forming sandstones of late Paleozoic age (~325-290 million years ago) cropping out in Garden of the Gods Park.  Unlike many other “famous” localities, the areas of geological interest in and near Colorado Springs are readily assessable to most people.  The rocks of majestic Pikes Peak may be observed along the Pikes Peak Toll Highway, US Highway 24 to Woodland Park, as well as along numerous secondary roads such as the Old Stagecoach and Gold Camp roads leading to Cripple Creek.  Garden of the Gods is a Colorado Springs city park readily accessed by several roads and trails.

With such world-famous sites available to all, we often overlook interesting localities in our backyard where both the causal observer and the dedicated hiker can get up close and personal with the rocks (it’s tough to get personal with the Peak). Virtually every Colorado Springs driver on I-25 has noticed such features as Pulpit Rock and Austin Bluffs associated with the north-south trending highlands of the Palmer Divide.  Those driving Centennial Blvd. and/or Vindicator Dr. are aware of the massive bluffs and upturned rocks of Popes Bluff.  But, how many people have actually stopped to examine some of these fascinating exposures.


The hogback or Popes Bluff looking north.

The Popes Bluff Area (PBA), including the adjacent highlands and hills of Ute Valley Park and the bluffs associated with Popes Valley Creek (along Popes Valley Dr.), is generally bounded by Centennial Blvd. on the west, Garden of the Gods Rd. on the south, Rockrimmon Blvd. and Vindicator Dr. on the north and I-25 on the east.  The bluffs and valley walls present numerous well-exposed outcrops of the Cretaceous Laramie Formation including abandoned coal mines, rock quarries, upturned hogbacks, and a large open space perfect for hiking, bird watching, and plant identification.  Jon Thorsen completed a geologic map of the Pikeview Quadrangle (Thorson and others, 2001) and readers should consult that publication for greater details. 


Rocks of Laramie Formation dipping east at Popes Bluff.

Rocks of the Laramie Formation, so well exposed in the PBA, represent the final regression of the vast Western Interior Seaway (WIS) that flooded what is now Colorado during much of the Cretaceous Period (~144 to ~65 million years ago).  The oldest of the local Cretaceous rocks, and unit representing the transgression of the WIS, are the complex of near shore marine, beach, deltaic, and estuarine sandstones (mostly) of the Dakota Group.  These rocks may be best known as the “Dakota Hogback”, a prominent topographic feature along much of the eastern flank of the Colorado Front Range.  The Graneros Shale, overlying the Dakota, is dark colored shale representing deepening waters (transgressing seas) and deposits of offshore mud.   As the seaway continued to deepen, the limestones and chalks of the Benton and Niobrara formations were deposited.  These limey muds were followed by deposition of thousands of feet of marine muds laid down many miles from the shoreline.  This mud became known as the Pierre Shale and is present under nearly all of eastern Colorado (Matthews, 2003).  Most of these Cretaceous rocks described above are well exposed in or near Garden of the Gods Park and Red Rock Canyon Park.  The Pierre Shale can readily be observed in the road cuts along Uintah Street leading west from I-25.

Perhaps 70 million years ago the early Rocky Mountains begin to appear and the WIS started its retreat from Colorado.  The beach sands of the regressive seas are known as the Fox Hills Sandstone and are not well exposed near the Bluffs; however, there is an exposure near Centennial Blvd about a mile north of its intersection with Vindicator Dr. (see Post  May 9, 2011)  Overlying the Fox Hills is the Laramie Formation, described below, while the end of the Cretaceous, and the beginning of the Tertiary (K-T), is marked by deposition of coarse sediments shed off the rising Rocky Mountain Front, the Dawson Formation.  One only needs to look east of I-25 at the Palmer Divide to observe these rocks (see Post November 27, 2012).

The Laramie Formation (description excerpted from Thorson and others, 2001) is a complex of rocks representing rivers, beaches, channel fillings, coal swamps, flood plains, lagoons, and estuaries---the sort of environments present along a regressing sea. At the entrance to Popes Valley (off Rusina Road) the road cut exposes a nice section of brownish-gray sandy shale and an organic-rick, dark-brown coaly shale; thinner beds of fine-grained sandstones also are present.  This sequence was probably deposited between river channels.  Above this section, and well-exposed on the north side of the valley, is a thick, light gray to light orange, crossbedded sandstone forming the valley rim (and holding up the houses).  This sandstone, and its counterparts, represents deposition in a river system and can be seen along Popes Bluff (from Centennial Blvd), and along the highlands and hiking trails within Ute Valley Park.


Road cut exposing Laramie Formation along I-25 at entrance of Popes Valley Drive.

One of the more fascinating sections of the Laramie Formation can be observed where Vindicator Dr. cuts through a hogback near Centennial Blvd. (by the vehicle driver), or at the western edge of Ute Valley Park (by the hiker).  At this locality forces associated with the rising Rocky Mountains have turned the Laramie Formation up to near vertical and a prominent hogback, held up by resistant channel sandstones, forms a spectacular topographic feature.  Along most of the hogback the beds are dipping to the east about 60 degrees.

 Near vertical beds of hogback (also associated with faulting).

Road cut along Vindicator Drive, a cut through the hogback.

During the late 1900’s and early 20th century, the mining of coal was somewhat of a major industry in and near Colorado Springs.  A number of coal mines operated in the PBA although I have been unable to locate much solid data on production.  Thorson and others (2001) produced a map showing perhaps a dozen known mines in the PBA.  Several old, but caved in, adits are visible along Popes Valley Dr. and in the adjacent stream valley to the north.  A very visible mine dump is easily seen about 1000 yards south of the Vindicator Dr.– Centennial Blvd. intersection.  The last mine to shut down in the PBA was the Pikeview Mine (total production of 8,738,174 tons) in 1957 and located off Delmonico Dr. immediately north of Rockrimmon Blvd (Thorson and others, 2001).  Also of interest is the fact that an oil well was drilled in the highlands near the mouth of Popes Valley.  The Rusina Ranch No. 1, spudded in 1959, was abandoned at a depth of 485 feet.  I was unable to locate information about a possible pay zone but perhaps operators were aiming for a sand zone in the Pierre Shale.  At any rate, the well was abandoned early.


Abandoned coal mine near Vindicator Drive.

Although fossils, including plants, dinosaurs, fish, turtles, amphibians, and mammals have been found at a number of Colorado localities, I am unaware of “good” body fossils in the PBA.  The carbonaceous shales of the Laramie Formation contain plant fragments and many sandstones contain macerated bones and plants; petrified wood (non-gemmy) is common.  Johnson (2002) noted that hard-to-identify dinosaur tracks are present in the area.  What the observer will notice, however, are numerous pseudofossils (such as nodules, concretions, and differential weathering), animal burrows, and sedimentary structures.

Ute Valley Park may be accessed from a parking lot off Vindicator Dr. or from a trailhead off upper Popes Valley Dr.  The best way to observe the geology is to take a stroll in the Park.  One never knows what interesting features will show up.

SOURCES CITED

Johnson, K.R. Ancient Denvers. 2002.   

Matthews, V., Lynn, K.K, and Fox, B., editors.  Messages in Stone: Colorado’s Colorful Geology.  Denver: Colorado Geological Survey, 2003.

Thorson, J.P., Carroll, C.J. and Morgan, M.L. Geologic Map of the Pikeview Quadrangle, El Paso County, Colorado. Denver: Colorado Geological Survey, Open-File Map and Report 01-3, 2001.
 




Sunday, April 3, 2011

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)2O3, 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.