Monday, November 14, 2011


Many of the rock and mineral clubs use the “silent auction” route as a way to raise resources for their many projects and groups.  Some clubs hold an auction monthly before their member meetings.  Others establish special days for a large auction.  For example, I note that the Colorado Mineral Society (Denver) holds their silent auction in early May while the Friends of Mineralogy (Denver) has an event in mid-May.  The Colorado Springs Mineralogical Society (CSMS) has at least one silent auction per year, and usually three.  The more formal, annual event is now held in the Spring.  In addition, the December monthly meeting features an auction, and the CSMS annual show held in June has numerous opportunities for picking up specimens via the auction route.  Receipts from the CSMS auctions are targeted for several of the Society’s groups, including the Pebble Pups and Juniors.  But to many rockhounds, the auctions are a prime time to acquire specimens for their cabinets at very reasonable prices.

One of the great “things” about club auctions is that many members are quite generous with their donations.  At other times, the club receives collections from the family of deceased rockhounds.  As a result, some auctions have very nice and beautiful specimens from exotic localities. During these last several CSMS auctions I have been able to acquire several minerals that I could not afford to purchase in shops or collect in far-away localities.

One of the “gems” that I recently acquired was a piece of brecciated chert? covered with radiating balls of green wavellite.  Wavellite is a hydrated aluminum phosphate mineral [Al3(PO4)2(OH,F)3·5H2O] that commonly appears in botryoidal and radial aggregates, a trait that makes specimens quite interesting.  Fairly soft at ~3.5-5.0, the mineral has a vitreous to silky luster and is translucent.  Although the green color is most impressive to me, it may be colorless to yellow and brown.  On the piece that I purchased several green sphericles were broken and therefore one may observe the radiating fibers.  Wavellite is most often a secondary or low temperature mineral found in vugs and fissures of the associated host rock.  It sometimes occurs with another green, hydrated aluminum phosphate, variscite (AlPO2· 2H2O).  Since the green color of variscite seems due to small quantities of Vanadium and Chromium (Foster and Schaller, 1966), I presume (out of my comfort zone here) that the green color of wavellite is due to the same elements.
My specimen was labeled “Montgomery County, Arkansas”, a fairly “famous” collecting locality near Mt. Ida. See Wavellite: Oct. 5, 2011.

Barite, or Baryte, is well-known to Colorado collectors since the state has several well-known localities.  The mineral is known for its variety of colors and crystal shapes and is a barium sulfate (BaSO4).  Barite commonly is secondary in nature, forming after the deposition/emplacement of the host rock, often from percolating ground waters or low temperature hydrothermal activity.  Barite is, to me, a fascinating mineral as it be may be found associated with lead, zinc and copper ores, and as Desert Roses (inclusions) in unconsolidated sands.  Most collectors identify barite by its “heaviness”, or high specific gravity.  I believe that the mineral has the highest specific gravity of any non-metallic mineral. 
 Near Colorado Springs, the Hartsel Locality has produced thousands of bladed specimens that occur as veins or layers in late Paleozoic rocks.  Most come from a single quarry located on private land and range in size from microscopic to12-13 cm.  Often clear in color when excavated, the crystals turn blue after exposure to sunlight.

The Book Cliffs north of Grand Junction, Colorado, have produced wonderful gemmy crystals of water-clear, terminated barite crystals from concretions in the Cretaceous Mancos Shale.  See Book Cliffs Barite: Jan. 3, 2013.

The Stoneham area in Weld County, Colorado, produces beautiful crystals of often-gemmy barite that are seen in rock and mineral shows throughout the U. S.  As at Hartsel, the barite is secondary and in this locality occurs in altered volcanic ash of the Tertiary White River Group/Formation.  I have never visited the collecting localities but hope to do so in the near future. 

Meanwhile, I was able to acquire several specimens via the auction route.
In my opinion, some of the most beautiful barite crystals in the state come from a locality known as “Muddy Creek”.  Located in Rio Grande County, Colorado, the crystals occur in vugs of a silicified, brecciated fault zone (Truebe, 1981).  One of the CSMS members has collected this locality and graciously contributed to the auction and I was able to acquire some museum-quality (my opinion) specimens.
Gemmy clear barite blades from Muddy Creek, Rio Grande County, Colorado.
 Quartz (SiO2) crystals are among the most common specimens on the market and appear in every auction.  However, I recently was the successful bidder on a very unique specimen from the San Vicente Mine in Guanajuato, Mexico.  The specimen has several large quartz points (~2.5 cm. in height) covered with very small siderite (iron carbonate, FeCO3) crystals and scattered water-clear calcite (CaCO3) crystals. Although most siderite is sedimentary in nature, I presume these crystals were formed via hydrothermal activity (I have been unable to locate much information about the mine). It is a beautiful and unique cabinet specimen. 
Quartz points, well-terminated, ~4 cm. (height) X 2 cm. (width) with scattered small crystals of siderite and water-clear calcite.  Specimen collected from the San Vicente Mine in Guanajuato, Mexico.
 A mineral related to siderite is rhodochrosite, a manganese carbonate (MnCO3).  There is a solid solution relationship between calcite, siderite and rhodochrosite.  What happens is that calcium, as well as iron, may substitute/replace the manganese; therefore, you get many different shades of pink and red for rhodochrosite and the exact chemical formula varies with the amount of manganese, iron, and calcium.  It is my understanding that “pure” rhodochrosite is rather rare.  See The Other Rhodochrosite: Oct. 9, 2011.

The most “famous” rhodochrosite” crystals are the specimens collected from the Sweet Home Mine near Alma, Colorado.  These rose-red colored crystals are prized by collectors the world over.  However, of interest to many rockhounds are the “sliced and polished stalactites” from the Capillitas Mine in Argentina. These specimens are very recognizable and occur as the principle gangue mineral in this lead-zinc sulfide mine.  The minerals are the result of hydrothermal activity in the late Tertiary and may be the largest mass of rhodochrosite ever discovered (The Giant Crystal Project, 2011).  I was able to pick up a couple of these slices and treasure them for their uniqueness. 
Massive rhodochrosite stalactites exposed in the Capillitas Mine, Argentina.  Photo courtesy of J. A. Saadi and The Giant Crystal Project.

.  Rhodochrosite (stalactites) from Capillitas Mine in Argentina. Specimens ~4 X 4 cm.
  It is not often that one is able to acquire turquoise at a club silent auction; however, CSMS received several “boxes of rocks” for liquidation and those “boxes” included specimens of turquoise.  As I remember, those nuggets and slabs were popular items at the auction, but I was able to pick up a nice pebble.  The mineral is generally thought of as a hydrous copper-phosphate mineral (CuAl6(PO4)4(OH)8·4H2O) and is a valued semi-precious gem stone; it usually is cabbed or mounted “whole”.  Turquoise is a secondary mineral developed during weathering and oxidation and usually occurs as a vein filling or as nuggets. I am uncertain about the collecting locality but the brownish-red matrix and the blue color certainly resembles Bisbee Blue.

Turquoise nugget ~3.5 cm. in length.  Unknown collecting locality.
 I once purchased a specimen labeled as “chalcotrichite, Campbell Shaft, 1800’-2300’ level, Bisbee, AZ”.  In doing some research on this partially-polished specimen, I found some interesting aspects concerning the mineral.  Chalcotrichite is “a variety of cuprite consisting of fibrous sprays or mats of hair-like crystals” (MinDat, 2011).  However, my specimen seems a composition of blood red cuprite (copper oxide, Cu2O), white calcite (CaCO3), and perhaps some native copper (Cu)—no hair like crystals are present. This specimen, collected from the Campbell Shaft or mine near Bisbee, Arizona, is known locally as campbellite. The mixture is valued as polished specimens or cabochons.  The mine seems a prolific producer of minerals and MinDat has listed 110 different minerals.  Mineralization at the Campbell Mine ore body is largely oxidized copper in Cambrian, Devonian and Mississippian limestones (MinDat, 2011).  At one time the underground mine was a major producer of copper and collectable specimens of azurite, cerussite and malachite. 
Polished “campbellite” from Campbell Shaft (~6 X 5 cm.).
 The Guanajuato, Mexico, Mining District (located approximately 175 miles northwest of Mexico City) is well-known to collectors of calcite, amethyst and quartz, and various sulfides of silver.  The area was “discovered”, or at least mined initially, in the mid-1550’s, and has produced a prodigious amount of silver, perhaps 44.5k U. S. short tons. That works out to about 89 million pounds of silver!  A further calculation would seem to indicate that with the current price of silver hovering around $50 oz., the total silver would be somewhere north of 7 billion dollars.  Wow.  These mines were the one of the major sources of funding for the Spanish Empire during their colonial rule of Mexico.

I have three beautiful specimens from the area picked up for very reasonable prices at various auctions.  One is a combination of large quartz points coated with micro-crystals of quartz and pyrite covered with finely pointed, translucent calcite scalenohedrons.  These crystals came from the La Sirena Mine.

Terminated quartz points (hidden on base in photo) coated with micro-crystals of quartz and pyrite covered with finely pointed, translucent calcite scalenohedrons (bright white).  Specimen ~8 X 9.5 cm.  Calcite crystals 1 cm. in height.  Collected Guanajuato, Mexico, Mining District.
 A second specimen is from the Peregrina Mine and is a large, waxy luster, stepped-face calcite scalenohedron sitting on a matrix of micro crystals of bladed calcite arranged in tiny spheroidal puffballs.

Stepped-face calcite scalenohedron (~1.5 X 4 cm.) sitting on a matrix of micro crystals of bladed calcite.  Collected Guanajuato, Mexico, Mining District.
 The third specimen, also from the Peregrina, is a matrix of small, sharply-pointed translucent quartz crystals holding, what appears to be, a large, step-sided calcite scalenohedron covered with small pointy quartz crystals.  It also appears to me that the calcite has been replaced by silica.  The numerous quartz points shimmer in the light. 

Cluster of sharply-pointed translucent quartz crystals.  Collected Guanajuato, Mexico, Mining District.
 My suggestion is to patronize the various silent auctions sponsored by rock and mineral clubs.  The camaraderie is always quite enjoyable and “bargains” often abound.

Foster, M.D. and W. T. Schaller, 1966, Cause of Color in Wavellite from Dug Hill, Arkansas: American Mineralogist, v. 51.

MinDat, the Mineralogical Data Base:

Truebe, H. A., 1981, Water-Clear Barite from Muddy Creek, Colorado: The Mineralogical Record, v. 12, no. 2.

Wallace, T. C., C. Francis, P. K. Megaw, Peter K.M, M.  Hall-Wallace, 1999, Silver Mineralogy of Guanajuato Mining District, Guanajuato, Mexico.(20th Annual FM-TGMS-MSA Mineralogical Symposium: Minerals of Mexico): The Mineralogical Record.