VIVIANITE FROM LEADVILLE, COLORADO

Vivianite is a hydrated iron phosphate mineral [Fe₃⁺⁺ (PO₄)₂-8H₂0] that is somewhat rare in Colorado except for the Treece and Ibex Mines in the Leadville Mining District. Eckel and others (1997) described vivianite from Leadville as among the “finest specimens of the mineral found in the country.”  Now, collectors of minerals from the Blackbird Mine in Idaho may wish to dispute that statement!  But I have not seen the crystals of vivianite (as long as 3 inches) housed in the Denver Museum of Nature and Science (Eckel and others, 1997) so will not cast my vote in either direction.

I have a few specimens of vivianite in my collection so at the recent Denver Spring Show I was not particularly looking for new samples.  However, in glancing at the tables a specific specimen popped into my brain since it was: 1) colorful crystals of vivianite (my other crystals are very dark, essentially black); 2) collected from Leadville; and 3) cheap at $2. It was further intriguing since my first line of information (MinDat.org on my cell phone) only showed five photos of Leadville vivianite and most were not something that I would write home to mama about.  The price certainly was right for someone who receives a monthly social security check, so it came home with me, and I consider it a good decision!

Vivianite is one of those interesting minerals containing the phosphate radical (PO₄) that I love to collect and “study.”  Phosphates are often grouped together with the arsenates (AsO₄), and vanadates (AsO₄) since these three radicals are about the same atomic size and frequently substitute for each other when combining with metal cations.  In some cases, there is a solid solution series between resulting minerals such as mimetite (lead arsenate)—lead phosphate (pyromorphite)---vanadinite (lead vanadate).  In others, the minerals are individuals and no solution series seem to exist.

Vivianite is a crystal of many colors, and in fact, can change color over its lifetime. Freshly exposed vivianite is generally colorless but with time oxidizes to green to bluish green to blue crystals.  Continued oxidation of the iron from Fe⁺⁺ (ferric) to Fe+++ (ferrous)  will produce crystals so dark blue they appear black.  Many crystals have a vitreous luster although they can grade into pearly or dull specimens.  Colorless crystals are transparent while lighter colored specimens become translucent and massive specimens generally are rather opaque. As with the color, mineral streak ranges from colorless to various shades of blue. Vivianite is quite soft, ~2.0 or less (Mohs).  The best “showy” specimens have prismatic (elongated along the C Axis) or flattened/bladed (along the B Axis) crystals and often form in stellate cluster; however, there are a variety of other morphological forms.

Matrix with indigo blue to purple crystals of vivianite.  Collected Treece or Ibex Mine at Leadville, Colorado.  Width of photo ~5.5 cm.

Photomicrographs from above specimen.  Width ~1.4 cm. 

Photomicrograph of broken and isolated cleavage fragment. Length along C Axis of longest fragment is ~5 mm.  S=sticky substance holding fragment on pine.

Vivianite is thought to occur as: 1) as a secondary mineral in metallic ore deposits; 2) in pegmatites as an alteration product of primary phosphate minerals; or 3) as a mineral associated with the phosphate found in sedimentary deposits. However, Petrov (2008) noted the mineral is not characteristic of the oxidized zone but of “deep unoxidized levels of ore deposits.”  I had assumed the crystals at Leadville were from the oxidized zone but am uncertain.

So, members of the Vivianite Group (shown below) include the iron arsenate vivianite, the zinc arsenate köttigite and the cobalt arsenate erythrite. 

Vivianite crystals (ex. Joe Dorris) collected Bingham District, Utah, a large porphyry copper deposit.  The largest crystal is ~2 cm. in length.

Mixed color spray of köttigite and water-clear selenite gypsum (S) and goethite (G).  Width FOV ~1 cm.  The variation and gradation of color may be due to an increase in iron substituting for zinc 

Mass of erythrite crystals.  Width FOV ~1.3 cm.

Vivianite is the namesake of the Vivianite Group of minerals that have a general formula of X₃(AO₄)₂-8(H₂O) where X is a ⁺⁺ metal (Mg, Mn, Fe, Co, Ni, Cu, Zn) and A is either phosphorus (a phosphate) or arsenic (an arsenate).  Most members of the Group are colorful and have weak ionic bonding resulting in mica-like cleavage.  Close relatives of vivianite include erythrite, a hydrous cobalt arsenate, and köttigite, a hydrous zinc arsenate.

REFERENCES CITED

Eckel, E. B. and others (revised edition), 1997, Minerals of Colorado: Fulcrum Publishing, Golden.

Petrov, A., 2008, A scientific study of the absorption of evil by vivianite: www.mindat.org/article.php/137/

DENVER SPRING 19 SHOW w/ BISMUTH & SULFOSALTS

The Spring Denver Gem and Mineral Showcase is a nice compact show held at the Crowne Plaza DIA along I-70 in “north” Denver.  The Show houses all dealers in a single large ballroom plus three dealers in adjacent smaller rooms.  There were somewhere around 75-80 dealers, by my quick count, although 7 dealers were wholesale only and I could not get by the “guard” to investigate!  At any rate, there was not an admission fee, parking seemed reasonable, and it was easy to navigate around the ballroom.  I thought the variety of sellers was very good judged on the very few dealers offering amethyst cathedrals, beads, and Moroccan trilobites. 

The main ballroom was well lite, and aisles allowed passage of disability chairs.  The tables were shallow enough to allow a good view of the selections. 

Three or four dealers were shuttled off to smaller rooms adjacent to the main hall.  This made for much confusion as many buyers were looking for the ever-popular Dan’s Used Rocks.

  I thought the orpiment (arsenic sulfide) on the left was a nifty specimen, especially when compared to the “crumbly” specimens on the right.  Of course, there is a major difference in cost per piece.

 

One could find specimens in all price ranges.

I thought the carved lapis animals different, but “cute.” 

What would a rock and mineral show be without beads?

In answer to the above question, the Show could start accepting Cannabidiol sampling booths.  I presume this CBD came from hemp rather than marijuana although this is Colorado!

This was my favorite specimen at the show as I love these phosphate nodules from Clay Canyon in Utah.

I was able to pick up a few minerals of interest from the show vendors including a couple of sulfides and a carbonate.

One of the sulfides has bismuth as the positive cation and is bismuthinite [Bi₂O₃], a major ore of bismuth.  It is a very soft mineral [~2.5 Mohs], has a metallic luster with a lead gray to while color, and is opaque. The mineral crystalizes in the Orthorhombic System, but most specimens appear as long prismatic to slender acicular crystals that are often flexible.  With weathering an iridescent tarnish usually is noted.  The crystals are often mistaken for stibnite (Trigonal Crystal System) to which it is related via solid solution—the bismuth being replaced by antimony. In addition, bismuthinite form a series with aikinite, a lead, copper bismuth sulfide. Bismuthinite, from the famous mines in Bolivia, forms in high-temperature hydrothermal vein deposit or tourmaline-bearing copper veins associate with granite.

Bismuthinite, with some marcasite coating, collected from Farralion Viejo Mine, Cerro Tazna, Bolivia. Width of photo ~ 2.8 cm.

 

Uber reflective partial crystals of bismuthinite.  Non-reflective crystals with a covering of marcasite.  Width of both photomicrographs ~1.2 cm.

 A carbonate, purchased at the Show, is somewhat scarce and is also a bismuth mineral:  Bi₂(CO₂)O₂. Bismutite is an oxidation product of sulfide bismuth minerals such as bismuthinite.  My specimen came from Rio Arriba, County, New Mexico, where pegmatites have been mined (mostly for Rare Earth Elements and thorium) from granites of Precambrian age in the Pteaca District. I presume the bismutite is simply a non-important secondary mineral.

Bismutite is a pretty non-descript mineral, at least to me, as the luster ranges from vitreous to dull and the color yellow to black.  Most specimens I have observed, including mine, are yellow-tan earthy mats or plates without observable crystal structures.  However, it does have a gray streak and is quite soft ~3.0 Mohs).  Probably the only way that I might recognize bismutite would be to realize that the hypogene sulfide bismuthinite was present in the deposit.

Yellow fibrous and crystalline bismutite.  Width of photomicrograph ~1.7 cm.

 

 Most bismuth used in industry comes from two sources: mining bismuth compounds, or as a byproduct of smelting other sulfides such as galena.  As for uses, most readers might recognize the anti-diarrhea medicine, Pepto Bismo (or one of its pink knockoffs).  Waterfowl hunters probably realize that bismuth (86% the density of lead) shot is a substitute for lead shot (to prevent lead poisoning). 

Two of my other postings have described minerals containing bismuth: mixite March 19, 2017), and pottsite (February 6, 2017). 

The second sulfide purchased was one completely unfamiliar but stumping me is not a real chore! At any rate dufrènoysite is an uncommon lead-arsenic-sulfide [Pb₂As₂S₅] with a metallic luster and a dark lead or steel-gray to dark red-brown color. It has a highly vitreous to metallic luster, especially on cleaved or fractured (brittle, mostly conchoidal) surfaces, is fairly soft (~3.0 Mohs) and has a red-brown streak.  The crystals are often elongated, parallel and striated.  But one small concern--dufrènoysite belongs to the Sartorite Group (with ~ 25 other minerals) and is described as A group of chemically and structurally very complex sulphosalts which are impossible to identify visually.  So, I assume it is dufrènoysite; however, I do not have knowledge of the crystal chemistry nor do I have access to sophisticated equipment. 

Sulfosalt minerals have a formula of AmBnSp where A represents a metal such as copper, lead, silver and iron; B represents a semi-metal like arsenic, antimony, or bismuth; S is sulfur. There is all sorts of substitutions by these metals and semi-metals.  For example, dufrènoysite, with arsenic, is in solid solution with veenite where antimony the major semi-metal.

Dufrènoysite  with dolomite crystals (rear) and a bright white  "sugar dolomite."  Width of photomicrograph ~1.3 cm.

Photomicrograph of above with one "shiny" crystal face.  Note stringer of chalcopyrite trending to upper left corner.

Photomicrograph of above, different angle. 

The specimen was collected by Michael Shannon in 1967 from the Lengenbach Quarry near Vallis, Switzerland (in the Alps), that MinDat describes as a “world famous metamorphosed sulphosalt/sulfide deposit in sugary dolomite.”  The quarry has yielded an amazing number of minerals (141) with 39 of these minerals claiming Lengenbach as their Type Locality (including dufrènoysite and a similar jordanite [described July 28, 2016]).  As best that I can determine, the quarry wall rock was originally Triassic in age until metamorphosed during the late Cretaceous-Tertiary.  A later hydrothermal event produced a solution enriched in arsenic, antimony and bismuth and also deposited the resulting minerals no sooner than ~11 Ma. 

I look forward to the many Denver fall shows running from around September 4 through September 15 at several building venues.  It is best to use an internet search engine for the latest information. 

TUCSON 2019: WULFENITE IS LOVED

After wandering around for nearly two weeks at the smaller ancillary Tucson shows the time came for the main event in the Convention Center (Thursday through Sunday).  I always try and attend the first day and did so this year.  As usual, a long line greeted us before the doors opened for attendees.  I buy very few minerals at the Convention Center since many/most of the specimens are larger and more expensive (and I have spent my allowance).  However, just walking around and looking/gazing at absolutely gorgeous specimens is enough to get the Adrenalin  pumping.  But one never knows as some dealers throw out a few cheaper ones that may not be selling online or their shop, and ones that might attract customers.  It often pays to be early in line on Day 1! And that is how I came to pick up a few other Arizona wulfenite specimens for my collection.

I probably have 80-100 photos of minerals exhibited or "for sale" in the main arena of the Convention Center; however, only a few of these will be displayed below.

Uncut gemstones are always a source of interest to me and I sometimes wonder what would happen if I were a faceter and messed up making a cut?  But raw gems are just as beautiful as cut  stones.

Heliodor is the golden-yellow variety if beryl (beryllium aluminum silicate).  Specimen from Zhytomor Oblast, Ukraine and priced at $45,000.

 Tanzanite is a blue to blue-violet gem variety of the the mineral zoisite (calcium aluminum silicate hydroxide). All tanzanite comes from Tanzania and "a significant percentage of ... crystals on the market have been heat treated ... to produce or enhance their color" (MinDat.org).

 

Morganite is the pink variety of beryl (beryllium aluminum silicate).  Specimen collected in Brazil.

Aquamarine is the sky-blue to sea-green variety of beryl (beryllium aluminum silicate). Specimen from Gilgit District, Pakistan and priced at $12,000. 

 Agates are always popular in show displays.  I thought the polished Laguna Agates (Mexico) were especially attractive.

 Since the show theme was Wulfenite is Loved one would expect plenty of specimens and visitors were not disappointed.

The wulfenite is this specimen for the Hilltop Mine in Cochise County, Arizona, is a distinctive yellow color.  The Hilltop was a polymetallic surface and underground mine discovered and first worked in the late 1800s.

Wulfenite from the Red Cloud Mine, La Paz County, Arizona (southwest Arizona), produced some of the most famous and expensive crystals of any mine in the world.  The red tabs are especially valued by collectors.

The two specimens above are from The Glove Mine, Santa Rita County, Arizona. 

Enlargement of above specimen.  Note the thickness of the individual tabular crystals.

Gold is always popular in the display cases.  These specimen came from the Colorado Quartz Mine, Mariposa County, California.

This amethyst specimen with the "crawling" calcite was one of my favorites at the Main Show.  Collected in Brazil. 

Long time Colorado Springs Mineralogical Society member and collector Ray Berry was remembered in this nice display case.

This seemed to be something new this year. Bottled varietal wine with labels displaying prints of actual mineral specimens.  The amazonite and smoky quartz specimen pictured on the bottle was collected near Lake George, a few miles west of Colorado Springs. 

The above two photomicrographs are wulfenite crystals from the Glove Mine, Santa Cruz County, Arizona.  The crystals are orange to light butterscotch color and are thick, simple and sturdy tabs. The large crystal in the upper photo is ~2.5 mm thick and 1.0 cm in length.

In contrast to the specimen above, this stack of dainty, transparent, window-pane, bevel-edge crystals is from the 79 Mine, Gila County, Arizona.  It is a beautiful specimen but unfortunately the digital camera could not pick up the yellow color of the crystals (light reflection).  Width of stack ~1.2 cm.

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