TUCSON INN SUITES: KARIBIBITE & FRANCKEITE

 The Arizona Mineral and Fossil Show at Hotel Tucson City Center has been a staple show for many years.  Many rockhounds refer to the show as the Inn Suites; however, changes are a coming. I certainly am not privy to the “real information” but vendors are leaving the Show and moving on due to—who know—contracts fights or something?  At any rate the “official” Show will move next year to the Hilton El Conquistador north of downtown Tucson in Oro Valley.  Some vendors have already moved to the Old Pueblo Show and also to the new Mineral City Show. I suppose we will know more in 2021.

The Arizona Mineral and Fossil Show has a couple of different formats: 1) the hotel rooms on two floors of a horseshoe shape arrangement are filled with vendors; 2) the “ballrooms” inside the hotel, and the lobby, have vendors, including some very large displays.  It seemed apparent to me that vendors have left for “greener pastures.”

The motel rooms, two stories, were not overly busy during my visit.  Many vendors were interested in visitors chatting about rocks and minerals.  I found Joe Dorris of Colorado Springs in one of these rooms; however, Joe had his crew scattered out in 4 or 5 different shows.

Other dealers occupied large ballrooms.

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Here is a dealer with a few tables outside the lobby.

Cenozoic sand dollars that seem pasted on the matrix?  Maybe not?

The "most popular" mineral from the last couple of years has been brucite.  It was still around in abundance this year but not as expensive.

Carved bowls, some quite large, were very popular this year.

How about a Pleistocene Lion?  Panthera leo spelaea from Romania.

Green River (Eocene) fish from Kemmerer, Wyoming are everywhere.  They are now preserved from collecting at Fossil Butte National Monument.

Black Hills Institute from Hill City, South Dakota, displayed some nice marine reptilian teeth. 

I did find a couple of specimens that were of interest, so they joined my collection: 1) karibibite with schneiderhöhnite and löllingite; and 2) teallite or franckeite.  As I noted in my previous text, life-long learning is just fun!

After numerous attempts I finally was able to get a decent photomicrograph of these sprays of karibibite. Each of these individual prismatic crystals are submillimeter in length.

So, what about the iron plus arsenic minerals? Karibibite is a beautiful, but rare, arsenite consisting of microscopic, orange yellow, sharply pointed, radial sprays of fibrous crystals usually less than 1 mm in length.  They are very soft and may be flexible and with a yellow streak. Karibibite is found in granite pegmatites and seems to be a weathering product of löllingite   but is often associated with schneiderhöhnite. Although it is awfully easy to call karibibite an iron arsenite (it is) the chemistry is quite complicated (at least for me) as there are two structurally different arsenite anions (the negative charged oxidation state); however, the numbers seem to “add up.”  Fe³⁺₃(As³⁺O₂)₄(As³⁺₂O₅)(OH) is the formula from MinDat.  So, the iron is 3+ x 3=9+ for the cation; the first anion is 3+ for the arsenic and the oxygen is 2 x 2- = 4- for a total of 1- times the 4 parts= 4-; and  the second anion is 3+ x 2= 6+for the arsenic while the oxygen is 2- x 5 =10- for a total of 4-; the hydroxyl is 2- for the oxygen and 1+ for the hydrogen= 1-.  The 9+ cation then is equal to the first anion 4-, the second anion 4-, and the hydroxyl 1-.  Please be aware that this little chemistry is just an exercise to??? Sharpen my brain, I guess.  It really does not be much to most rockhound readers. 

Several sprays of karibibite housed in very reflective löllingite.

Karibibite is almost always found in vugs of löllingite, an arsenide—iron plus arsenic, FeAs₂.  Again, the iron 2+ is the positive cation while the arsenic 1- serves as the negative anion (arsenic has a variety of oxidation states).  Trying to describe löllingite is sort of tough.  It is a shiny, silver-white to steel-gray mineral with a metallic luster, a medium hardness of ~5.0-5.5, has a gray-black streak, is brittle, and has an “almost” conchoidal fracture.

Sprays of karibibite surrouned by löllingite with the dull metallic luster of schneiderhöhnite in lower right quadrant.

Karibibite also is commonly found with the schneiderhöhnite, an arsenite that contains both ferrous (oxidation state of 2+) iron and ferric iron (oxidation state of 3+):  Fe²⁺Fe³⁺₃As³⁺₅O₁₃.  The iron content imparts a black to brownish black color and a resinous to dull metallic luster.  At Mohs 3 it is softer than the 5.5 of löllingite and I used that property as a major identification tool.  It has a brown streak, is brittle and a platy/micaceous fracture. An old label indicated my specimen was collected from the Urucum pegmatite at Galilela,Minas Gerais, Brazil.

The second mineral that I picked up is labeled teallite, a lead tin sulfide---maybe!  The specimen was collected by David Shannon several decades ago from the San Jose Mine in Oruro Department, Bolivia.  MinDat states that “a great many specimens labelled teallite, especially those from the San Jose mine in Oruro are really franckite [iron lead tin antimony sulfide]…Franckeite from here is frequently mislabeled and sold as teallite.”  So, I am going with my specimen as franckeite (Fe(Pb,Sn)₆Sn₂SbsS₁₄)  with some minor jamesonite, a lead iron antimony sulfide (Pb₄FeSb₆S₁₄). 

Crystals of franckeite with a top layer of the needle-like crystals of jamesonite.  Essentially impossible for me to get a decent photo of this reflective mass of mixed up crystals.  I just don't have the equipment. Width FOV ~ 1.4 cm.

Photomicrograph of franckeite crystals with a small mass of jamesonite in upper right corner.

Franckeite is quite rare and an opaque mineral with the metals imparting a black to gray-black color and a metallic luster.  Typical of the metallic minerals, franckeite has a gray-black streak and is malleable. Crystals may be thin tabular, foliated, fibrous, massive or aggregates and fine-grained, or stellate. The cleavage flakes  are flexible and the metallic luster reflects light (like many metals).Franckite is soft at ~2.5 (Mohs). The mineral is found where carbonates encounter metamorphic rocks (contact metamorphism) and in polymetallic rocks reacting to hydrothermal fluids.

Jamesonite is a dark gray mineral that is common as masses of needle-like acicular, prismatic crystals.  It is soft at 2.5 (Mohs). It has a metallic luster and is opaque. It is a hydrothermal mineral and sometimes occurs with boulangerite (which it resembles).

The next series of Tucson Shows in 2021 will certainly be different for the Arizona Mineral and Fossil Show.  Will it be at the Tucson Center?  At Mineral City? El Conquistador Hilton?  Only time will tell.

Sometimes the questions are complicated, and the answers are simple.       Dr. Seuss