The Tucson shows are “done gone” and were a big success, at least from my point of view. I was able to spend every day for two weeks exploring the different venues and making a purchase or two. The Tucson “main show” occupied two full days of my time trying to digest the exhibits and ogling at the many specimens offered to buyers. In addition, I spent several hours over 4 days up at the Mineral City event as documented in recent Posts. In moving on from the venues at Mineral City I next visited what is probably the most authentic show left in Tucson, the Miners Co-op Rock Show located west of I 10 at Mike Jacobs Sports Park. When I say authentic, I mean what many venues looked like several decades ago---grass and gravel, free parking, vendors selling from pickup beds, tents, open air tables, small trailers, cooking meals over a small propane stove, and living quarters in small RVs parked directly behind their displays. The rains come and tarps or plastic unfurl to cover the tables. Here comes the welcome sun and off come the covers. There seems to be a camaraderie among the dealers, and all seem very willing to spend time visiting with the lookers and buyers. I usually see the same dealers every year including CSMS members Kim and Bodie from Runnin Boar Minerals selling locally derived amazonite from their mines.
Black montroseite mixed with corvusite on the surface and in pores of quartz-rich sandstone. Width FOV ~5.0 cm.
I did not find many specimens to tweak my interest but did come home with a specimen of an ugly black mineral collected from one of the uranium-vanadium mines on the Colorado Plateau. Without looking at the label I thought it probably was corvusite, a nondescript hydrated sodium, calcium, potassium, magnesium, iron and vanadium oxide (and also pretty ugly): (Na,K,Ca,Mg)2(V5+V4+Fe2+)8O20--6-10H2O [For a better description see November 10, 2019 posting]. However, my purchased specimen (black to grayish black) was identified as montroseite, a vanadium iron oxide hydroxyl [(V3+Fe3+)O(OH)] or sometimes labeled as a vanadium oxide [V3+O(OH)]. Although these two minerals, corvusite and montroseite, might look similar, and they are often intermixed in a single specimen, the iron in corvusite is ferrous iron with a charge of 2+ while montroseite is the 3+ ferric iron. In addition, corvusite has water, H2O, while montroseite has a hydroxyl molecule. The vanadium in corvusite has charges of both 4+ and 5+ while montroseite has 3+ vanadium.
My specimen was collected from the Burro Mine, Slick Rock District, San Miguel County, Colorado [the Type Locality of 12 minerals]. In fact, the reason I purchased the specimen is that montroseite is a Colorado Native as the Type Locality is the Bitter Creek Mine, Uravan Mining District, Montrose County, Colorado [located just north of the Burro Mine in San Miguel County] (Weeks and others, 1951, 1953).
Montroseite is tough to identify without some gizmo like XRD. It is black to gray black in color with a black streak and a less than metallic luster (sort of a dull metallic). It is fairly hard at ~ 6.0 (Mohs). If one can locate crystals, they might be bladed and or striated. Unfortunately, I have had an extremely difficult time locating good crystals as the vanadium minerals present in/on the sandstone matrix are massive or seem to fill tiny pores between the grains of sand (essentially quartz).
Here is another problem that I can’t fix without an XRD. Montroseite seems to rapidly transform to paramontroseite {V4+O2] when exposed to air—paramontroseite is a pseudomorph after montroseite, and also has its type locality at the Bitter Creek Mine. Paramontroseite results from the oxidation of montroseite in a solid solution relationship. Oxygen, either in groundwater of in the air, oxidizes montroseite in temperatures under 50 degrees Celsius and the hydrogen escapes: 2V3+O(OH) + 1/2O2à2V4+O2 + H2O (Evans and Mrose, 1955).
But then, paramontroseite is also unstable and weathering causes numerous other minerals to form, depending upon chemical weathering conditions: mostly corvusite but also hewettite, hummerite, pascoite, rossite, and simploite (Garrels and Pommer,1957). When montroseite “changes” to paramontroseite the crystal structure essentially remains intact. When paramontroseite weathers its crystal structure is destroyed and new minerals form.
The exact source of the original vanadium in these deposits is somewhat uncertain; however, Thamn, Kovschak and Adams (1981) noted the “Salt Wash [Member of the Jurassic Morrison Formation] deposits are essentially vanadium deposits, but as yet no convincing case has been made for the source of that vanadium. Favorite hypotheses suggest that it was (a) derived from altered llmenite and magnetite, (b) introduced diagenetically from the overlying Cretaceous sediments, or (c) was derived from the leaching and erosion of Paleozoic sediments well to the west of the Colorado Plateau. All of these hypotheses are, to some extent, plausible, but are as yet unsubstantiated.”
Well, there you have it. I purchased the specimen due to the type locality located out in the uranium beds of western Colorado in Montrose County. Unfortunately, I can’t really tell if it is montroseite or paramontroseite or perhaps it has started to weather into another vanadium minerals. When one looks at the Bitter Creek specimens on MinDat it seems impossible to separate montroseite from paramontroseite. However, MinDat only lists a single specimen of montroseite, no paramontroseite, from Burro Mine, and that photographed specimen looks “just like my montroseite.” I also noted that the MinDat’s photo’s description (written by specimen owner Andrew Hodgson) stated: Old Material, purchased from Ralph Merrill (Minerals Unlimited) in 1983. Interestingly, the label on my specimen is very fragile and faded (indicating old) and is from Minerals Unlimited with a price tag of $50! And so I will leave it at that---a learning experience,
REFERENCES CITED
Evans, H. T., Jr . and Mrose, Mary E., 1955: American Mineralogist, v. 40.
Garrels, R. M. and Pommer, A. M., 1956, Some quantitative aspects of the oxidation and reduction of Colorado Plateau ores: U.S. Geological Survey Trace Elements Investigations Report 177.
Thamm, J.K., Kovschak, A.A. Jr., and Adams, S.S., 1981, National uranium resource evaluation. Geology and recognition criteria for sandstone uranium deposits of the salt wash type, Colorado Plateau Province. Final report: United States: N. p., 1981. Web. doi:10.2172/6512174.
Weeks, A.D., Cisney, E.A., Sherwood, A.M., 1951, Hummerite and montroseite, two vanadium minerals from Montrose County, Colorado. Abstracts of papers presented at the thirty-first annual meeting of the Mineralogical Society of America at Washington, D.C: American Mineralogist, v. 36.
Weeks, A.D., Cisney, E.A., Sherwood, A.M.,1953, Montroseite, a new vanadium oxide from the Colorado plateaus: American Mineralogist v. 38.
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