VALENTINITE: SECONDARY ANTIMONY MINERAL

 

In an earlier posting (August 21, 2020) I described my specimen of senarmontite, an antimony oxide [Sb₂O₃] that often appears as nice octahedral crystals (Isometric System). It usually has a gray to white color or occasionally red to colorless.  The colorless variety is transparent while the others are translucent to mildly opaque.  Although my specimen is a nice octahedron, senarmontite also occurs as a massive and or granular mineral. Colorless crystals are subvitreous while others have a resinous luster, but all have a white streak.  The mineral also is quite soft at ~2 or a little more (Mohs).

The octahedron of translucent senarmontite.  Width/length crystal ~7 mm.   Specimen collected from  the Djebel Hammimat Mine, Ain Babouche District, Oum el Bouaghi Province, Algeria.

It is always interesting as a rockhound to locate dimorphous minerals, that is minerals with the same chemical formula but crystalizing in different Crystal Systems. So, I was happy to pick up two specimens of valentinite, also an antimony oxide with the same chemical formula as senarmontite [Sb₂O₃]. However, valentinite is a member of the Orthorhombic Crystal System and usually appears as flattened prismatic crystals with complex terminations in fan-shaped aggregates. Most minerals have an adamantine luster, a white streak, and are colorless to white; collectors like to locate rarer yellow, pink and brown crystals, However, as in senarmontite, valentinite may form in granular masses.

The specimen above was collected from the Graf Jost-Christian Mine, Wolfsberg, Sangerhausen, Mansfeld-Sudharz, Saxony-Anhalt, Germany. The mine started extracting antimony ore around 1700. There are tiny acicular crystals on porous quartz crystals. MinDat noted specimens from here are rare. The original label, from Shannon’s Minerals in Tucson was glued on but appears “older,” I remounted the specimen due to the condition of case. Width FOV top is ~9.5 mm. With of bottom specimen ~3.0 mm.

Flat lying radiating sprays of valentinite on a stibnite matrix. Width FOV ~1.7 cm. Collected from Kolarsky vrch deposit, Pezinok, Pezinok District, Bratislava Region, Slovakia. MinDat noted “One of the largest hydrothermal antimony deposits in Slovakia. Small-scale mining of antimony started in 1790 and after some breaks finally stopped in 1991 for economic reasons. The deposit is famous for excellent kermesite specimens. Vein-type antimony deposit, hosted in Late Silurian to Lower Carboniferous phyllites and black slates.”

Both senarmontite and valentinite are secondary minerals and are  weathering/alteration products of other antimony-bearing minerals (commonly stibnite) in the oxidized zone of hydrothermal antimony deposits. Associated oxidized minerals often include stibiconite [Sb³⁺Sb⁵⁺O₆(OH)], cervantite [Sb³⁺Sb⁵⁺O₄], and kermesite [Sb₂S₂O].

A brief word about dimorphic polymorphism—brief because understanding the exact mechanisms causing such are mostly above my pay grade. I best understand the dimorphs calcite and aragonite (high pressure polymorph). However, aragonite is metastable at the low pressures near the Earth's surface and is thus commonly replaced by calcite. In fact, aragonite is rare or absent in rocks older than ~Mississippian age. Many rockhounds "sort of" understand carbon (hexagonal structure) and diamond (isometric structure) where differing pressure and temperature form different minerals. I "sort of" understand that the dimorphism in senarmontite and valentinite evidently is in response to changes in temperature and pressure during their formation. Senarmontite seems to be metastable; however, I don’t have the slightest idea if  there can be a change to valentinite. I just cannot locate appropriate informative literature so will file that problem in “one of life’s persistent questions.”

READY TO BUY; READY TO SELL: DENVER 2023

I had the opportunity to attend one day, a very loooong day, of the Spring Denver show at the Crown Plaza DIA. My initial impressions were: 1) it was a very large show and I counted over 100 dealers; 2) prices continue to move upwards, just as groceries and my home utility bill; 3)  the Friday show attracted a large crowd. 

I came home with only a few specimens and will post them in the near future. However, I did want to throw out a few photos of the show.

Ready to buy at the opening bell!!!!

Ready to sell, let them in!!!!

Boxes of attractive shattuckite, a copper silicate [Cu₅(Si₂)₆)₂(OH)₂ ] from Democratic Republic of Congo (boxes are labeled Zaire). Most are in the $200 range.

Not many minerals to excite here, just playing tunes on the metal bowls. Not for me as I flunked finger cymbals in the grade school rhythm band.

Hematite included quartz from Morocco, Dan & Barb Stephens. 

$100.

Halite from Searls Lake, CA.  Dan & Barb Stephens. 

$125.

Dennis Beals of Colorado (Denver area)  had this beautiful specimen of calcite from Santa Eulalia, Mexico. Dennis is always good for a wild tale or two about his southern collecting trips. 

Binghamite  is a lapidary term referring to a rock consisting of fibrous amphiboles intergrown with quartz. The amphiboles are mostly altered to a complex mix of quartz, siderite, and various iron and manganese oxides such as hematite and goethite. Rough material comes from the iron range mines in Crow Wing County, Minnesota. Info from MinDat.

Phil from Persson Rare Minerals (Denver area) sorting out his display case. Nice specimens.

Do you like earrings? I saw several displays such as these faceted  minerals (maybe some synthetics?)

 

Nice displays of fossils. Read an interesting article about selling vertebrate fossils collected in China at https://www.fossilhunters.xyz/ (updated April 15th, 2023).

Boxes and boxes of pretty minerals flooded the floor.

Maybe the most reasonable price all day on faceted stones.

Tourmaline Group (mostly elbaite) specimens for sale at many booths.

I always like polished labradorite with the iridescent effects. Usually out of my price range!

As usual, the "guard" at the gate would not let me sweet talk my way into the Wholesale Section of the Show where Dan's Used Rocks was hiding.

Colorado Springs dealers Joe Dorris (Pinnacle 5 Minerals) and Leonard Himes never miss a show. My photo of Austin and Kevin from the Springs turned into a big blur. Sorry.

And if all those faceted gems and semi-gems did not get you excited, there were always magic minerals to peruse. External of the show one might be able to buy magic weed and perhaps scrounge up some magic shrooms--after all this is Colorado, a pretty magic place to live. Travelers, just remember to clean out your luggage before flying home 😁😁😁