MORE PESKY VANADIUM MINERALS: MOTTRAMITE, DESCLOIZITE, ROSSITE & STRACZEKITE

The last couple of Postings have focused on minerals containing the element vanadium.  Although many rockhounds recognize the name vanadium, that is mostly due to the bright red, popular mineral vanadinite; most rockhounds (including me) don’t know an awfully lot about other minerals containing vanadium.  That is one reason that I have taken an interest in the group of minerals termed the Phosphates, Arsenates and Vanadates—trying to learn about some of the uncommon minerals.

Vanadium (V) rarely occurs in nature as a native element [it is found in fumaroles of the Colima Volcano in Mexico (Ostrooumov and Taran, 2015)]  and most vanadium-bearing minerals are not mined specifically for the vanadium, the exception being patronite, [vanadium sulfide, VS₄] mined early in the 1900s from Peru.  However, vanadium is an important industrial mineral used to harden steel and today is produced as a byproduct of steel production (slag, magnetite), or from uranium mining and milling.

Although vanadium may seem to be a rare element, it is the 20^th most abundant element in rocks of the earth’s crust.  Vanadium compounds occur in about 65 different minerals (Strumfels, 2019)---or take your choice---there are187 valid species containing essential vanadium [1 element, 8 sulfides and sulfosalts, 69 oxides, 10 sulfates, 69 vanadates, and 30 silicates] (mindat.org). Vanadium has a number of oxidation states, 3-, 1-, 1+, 2+, 3+, 4+, 5+ with the 5+ being the most common state in minerals where it often combines with 4 oxygen ions (2- each) to form the anion VO₄ with a 3- oxidation state, the orthovanadates. However, there are a number of other minerals where cations (metals) are combined with other vanadium anions. And synthetically, there are a gazillion different compounds that I don’t even pretend to try and understand.

So, in sorting out my minerals I wanted at least get a photo of vanadium-bearing minerals in my small collection.  By calling up the two web sites listed above, MinDat and Strumfels, readers will notice the rarity and unknown names of most listed minerals, at least they were mostly unknown to me.

Among the orthovanadates [VO₄ ion with 3- charge] I have written about pottsite (Feb. 6, 2017) (hydrated lead and bismuth vanadate [(Pb₃Bi)Bi(VO₄)₄-H₂O]), pucherite (October 15, 2019) [Bi(VO₄)], vanadinite (Feb. 4, 2015) [lead chlorvanadate [Pb₅(VO₄)₃Cl] and mentioned the uranium mineral carnotite [K₂(UO₂)₂(VO₄)₂--3H₂O] several times (I shy away from uranium).  But two very common orthovanadate minerals are descloizite [PbZn(VO₄)(OH)] and mottramite [PbCu(VO₄)(OH)]

and there is a solid solution series between the two.  In fact, it appears that neither mineral is actually “pure” in that descloizite always has “some” copper while mottramite contains some amount of zinc.  For example, at one time rockhounds recognized a mineral known as cuprian descloizite collected from Mexico or Namibia and zincian mottramite from Angola.  Manganese and iron also may substitute for copper and/or zinc while arsenic, phosphorus and molybdenum may replace some of the vanadium (Millman, 1960) as in the discredited mineral dechenite, an arsenian variety of descloizite. It is very difficult for me to differentiate these minerals as both appear in polymetallic mining areas where vanadium, copper and zinc are available.

I have photos of two specimens of descloizite, one from the Whale Mine near Goodsprings, Nevada and a second from the Mammoth-St. Anthony (Tiger) Mine in Arizona.

Descloizite [PbZn(VO4)(OH)] appears in a variety of colors, black, blackish-brown, reddish brown, and reddish orange mainly due to the differing amounts of lead, zinc, copper and iron in the chemical makeup. The luster ranges from vitreous to waxy and greasy but readers will often observe the descriptive term sparkly. It is soft at ~3.0-3.5 (Mohs) and translucent to transparent.  The streak I received on a porcelain plate is brownish red to orange.  Crystals are tough to describe on many specimens and range from “squat” pyramidal to prismatic but then some are very tiny intergrown fibers. 

Descloizite, Goodsprings Mining District.  Width FOV 5 cm.

   

Photomicrograph of submillimeter crystals from above specimen. Width FOV ~ 9 mm. Some crystals have faces while others appear as elongated ?fibers.

The Goodsprings Mining District is located near Las Vegas and the first mine was developed around 1856 by lead miners sent out by Brigham Young, the LDS President housed in Salt Lake City. There is not much information on the early history of the District; however, several small-time miners toiled to bring out a few tons of lead ore each year.  Transportation of the ore to smelters was a problem and local “furnaces” had difficulties collecting high grade lead due to “contamination” by zinc.  Transportation improved in 1905 when a main line of the Los Angeles-Salt Lake Railroad zoomed by a few miles from the main group of mines.  Then in 1911 a branch line reached the residents and mines of Goodsprings and by 1916 around 800 hardy persons lived and worked the mines. By then zinc had become the biggest commodity but in 1915 the price of zinc started to decrease and by the end of the decade few people remained, and the largest mines had closed. However, there were small spurts of renewed mining activity during World Wars I and II with final production around mid-century. Today the Pioneer Saloon is a drawing card for tourists roaming the desert.  In addition, there are still several hundred ?active claims with prospectors hoping for that pot of gold, or for any of the other previously mined commodities—silver, copper, lead, zinc, vanadium, molybdenum, cobalt, nickel, uranium, platinum or palladium. The Nevada Historical Society estimated the mines produced about 25 million dollars’ worth of metals; however, I am not certain about this figure—dollars in what year.

The Whale Mine was one of the smallest mines in the District and the last known production of zinc (hydrozincite, hemimorphite) and lead (wulfenite) was in 1943.  These are secondary hydrothermal minerals found in Mississippian limestone hosts.

The second specimen of descloizite in my collection comes from the Mammoth-Saint Anthony Mine (AKA Tiger Mine), Mammoth Mining District, Pinal County, Arizona.  The Tiger, as locals like to call it, is one of the best-known mines in Arizona and is located about 50 miles northeast of Tucson.  MinDat noted of the 108 valid minerals that have been collected at Tiger, 10 list the mine as their type locality.  The property had both underground and surface mining but was finished by sometime in the 1950s.  A few years ago, I visited the area and was not permitted anywhere near the past mining sites and all structures seemed demolished and pits and shafts were filled in.  What remains is a small population living in the community of Mammoth.  However, although the mines disappeared over a half century ago, it seems quite easy to purchase specimens from the Tiger, especially wulfenite. 

Descloizite from Mammoth-St. Anthony Mine.  Width of specimen ~2.1 cm.

Photomicrograph showing crystals of descloizite from above specimen.  Width of specimen ~ 1.1 cm and showing a "more true" color.

The mines at Mammoth were polymetallic in nature and evidently metal-rich hydrothermal fluids deposited ores along fault and shear planes.  Over the years the mines produced approximately 400,000 ounces of gold, 1,000,000 ounces of silver, 3,500.000 pounds of copper, 75,000,000 pounds of lead, 50,000,000 pounds of zinc, 6,000,000 pounds of molybdenum oxide, and 2,500,000 pounds of vanadium oxide (Howell, 1991).

The descloizite specimen labeled “Tiger” is a mass of individual crystals that is vitreous to subvitreous and transparent to translucent.  The best that I can describe the crystals is compressed to squat pyramids.  And, the specimen is very difficult to photograph, at least with my equipment, due to light reflection.  The crystals really do not look like other descloizite specimens that I have observed from Tiger but more closely resemble groups of crystals from Namibia.

So, on the other end of the spectrum is the copper analogue of descloizite, mottramite.  But again, some of the specimens of this mineral are tough for me to identify with certainty.  The grass-green to yellow-green specimens are certainly easier to name than the blackish-brown to black crystals.  Some of these darker crystals greatly resemble descloizite (at least to me). Mottramite is a soft mineral ~3.0-3.5 (Mohs) and has a yellowish-green streak.  Crystals range from transparent to opaque.  They are less “sparkly” than descloizite crystals and are often described as having a waxy or oily luster. Mottramite often forms encrustations or botryoidal/mammillary masses. 

Width FOV ~3.5 cm.

Width FOV ~1.2 cm.

                Width FOV ~7 mm.

Three photos above. Deep olive green botryoidal mass of mottramite partially covered by submillimter (really tiny) masses of black fibrous crystals of “something.”  They are so small that neither my microscope nor digital camera can help me identify the buggers.  However my best guess is that there are a second growth of mottramite (take a peek at photo on MinDat.org, F35-XU1 shot by Steve Rust, page 4 of the photos).

Botryoidal mottramite (I think) from Glove Mine in Arizona.  Something like manganese providing black covering. Width FOV ~1.1 cm.

The specimens I have are a nifty green encrustation on shattuckite from Namibia, and botryoidal forms from Namibia and Arizona.  The most attractive of these specimens is a bright green (grass green) encrustation of mottramite on a light sky blue, fibrous to spheritic mass of the rare copper silicate, shattuckite [Cu₅(Si₂O₆)₂(OH)₂] from the Kandesci Mine, Kunene Region, Namibia.  It seems as although the Kandesci Mine is world-famous for specimens of shattuckite, the discovery of mottramite on shattuckite is relatively new.

Green mottramite encrusting blue shattuckite.  Width FOV ~2.5 cm.

The Tsumeb Mine in Namibia, well known for specimens of mottramite, is one of the most recognizable mines in Africa. MinDat states the Mine is “renowned for a wealth of rare and unusual minerals” with 299 valid minerals that includes the type locality of 72 minerals.  It was (1907-1996) a polymetallic ore producer but was first developed as a copper mine.  The numerous rare and secondary minerals found in the Mine are mainly due to the fact that three different oxidation zones developed over time on/in the pipe-like ore body (Precambrian carbonates).

The minerals noted above all contain the VO₄ Ion (3- oxidation state). 

In my collection I found another vanadium mineral, straczekite [Ca,K,Ba)(V⁵⁺V⁴⁺)₈O₂₀-3H₂O] that is chemically related to corvusite described in a previous Post (Nov. 10, 2019) since both contain V₈O₂₀ ions with a 4- oxidation state.  The straczekite was picked up at a Tucson show and was collected from the Union Carbide Pit, its Type Locality in Arkansas, in an area called the Wilson Springs Vanadium Deposit (previously referred to as Potash Sulfur Springs).  Hollingsworth (1967) described the geology of the vanadium deposit as being “near a contact zone between folded Paleozoic country rock and the Potash Sulfur Springs intrusive complex, in a setting that is similar to that characteristic of the Magnet Cove intrusive about six miles to the east. The vanadium constitutes about 1% of the ore, erratically disseminated in altered alkalic igneous and metamorphosed sedimentary rocks.” The Mine (four open pits) opened in 1966 and closed in 1985 producing vanadium and niobium-columbium that evidently was enriched by hydrothermal and weathering processes.  Evidently all of the vanadium was produced from straczekite, hewettite [calcium vanadium oxide, V₆O₁₆)], duttonite [hydrous vanadium oxide, VO], fervanite [hydrated iron vanadium oxide, V₄O₁₆] and schoderite [aluminum phosphate vanadate]. I find it interesting that this small mine has produced: 1) 72 different minerals including three type localities: malhmoodite (hydrated iron zinc phosphate), miserite (complex hydrated potassium REE silicate), and straczekite; and 2) vanadium that was mined from very unfamiliar and somewhat rare minerals. 

Photomicrograph of straczekite crystals. Width specimen ~8 mm.

 Photomicrograph of straczekite crystals. Width FOV ~7 mm.

Straczekite [Ca,K,Ba(V⁵⁺,V⁴⁺)₈O₂₀-3H₂O, is a calcium barium potassium vanadate that occurs as a rare secondary mineral in fibrous seams in gangue at Wilson Springs and three other localities (single mines in Utah, Arizona and Germany). The crystals are dark greenish-black in color, have a greasy luster and are very soft (1-2 Mohs). They generally appear as thin laths up to 0.5 mm in length that form masses (Evans and others, 1984).

The dark color of straczekite indicates that vanadium is present as a mixture of valence states V⁴⁺ and V⁵⁺.  During the discovery phase of straczekite Evans and others (1984) noted that its crystal chemistry [V₈O₂₀] seemed not to “fit” with other known vanadium minerals; however, it was identical to a series of anhydrous synthetic layer vanadates known as vanadium bronzes. Zhang and others (2000) believed the V₈O₂₀ layers are composed of equal numbers of VO₄ tetrahedra and VO₅ pyramids connected by both corner and edge sharing. That is my limit of knowledge of vanadium crystal chemistry.  Don’t try to digest it, I just wanted to get it down on paper as a learning exercise to keep my brain functioning. 

Another vanadium mineral I picked up in Denver is rossite, a rare calcium vanadate tetahydrate: Ca(VO₃)₂-4H₂O.  Here the vanadium has a 5⁺ oxidation state so the ion VO₃ (metavanadate ion) has a 1- state. However, rossite often/mostly dehydrates (loses water by heating) and forms the metavanadate dihydrate, metarossite: Ca(V₂O₆)-2H₂O where the (V₂O₆) ion has an oxidation state 2-. This chemical reaction is also reversible.  It is interesting to note that Foshag and Hess (1928), the scientists who discovered and named these two minerals, could not identify crystal forms in rossite so they dissolved the rossite in water, dried it to form metarossite, and then added water and reconstituted rossite crystals. Most occurrences of these two minerals is in carnotite (uranium ore) veins.  In describing the Colorado Plateau uranium deposits, Evans and Garrels (1958) believed that “montroseite [(VO(OH)] is evidently the primary mineral source of vanadium.”  

Photomicrograph pale yellow rossite with nearly colorless metarossite.  Width FOV ~1 cm.

Rossite is a very pale yellow to white, vitreous to pearly, transparent to to translucent, soft (2.0-3.0 Mohs) and forms “lumpy” crusts that almost always shows some alteration to metarossite.  The latter mineral is very soft at 1.0-2.0 (Mohs) and is more likely to form platy or flaky crystals.  Color ranges from pale yellow to colorless/white.  Both minerals belong to the Triclinic Crystal System.  My specimen was collected from the Sunday Mine (Sunday #2), Uravan Mining District, San Miguel County, Colorado.  Many of the mines in the Uravan District, including the Sunday, mined ore from the Jurassic Morrison Formation (formerly referred to as McElmo Sandstone).

Photomicrograph of nice crystals of metarossite covering left half.  FOV ~1 cm.

In precious posts I have written about cavansite (Feb. 24, 2016) [hydrated calcium vanadium silicate Ca(VO)(SiO₄O₁₀)-4(H₂O)] and its dimorph, petagonite, the nice blue minerals rockhounds love from the Pune District of India.  Both minerals include the oxovanadium cation VO2+ where the vanadium has a 4+ oxidation state while the single oxygen is 2-.  This is one of the few vanadium cations (positive oxidation state).  Sincosite [Ca(VO)₂(PO₄)₂-5H₂O] a hydrous calcium vanadyl phosphate from the Black Hills (Dec. 2, 2018) also employs the VO cation.

And finally, the other vanadium mineral in my collection is volborthite (hydrated copper vanadate hydroxide [Cu₃V₂O₇(OH)₂—2H₂O]) that uses the pyrovanadate ion [V₂O₇ with an oxidation state of 4- where the vanadium is a 5+].  The specimen was collected from Taos County, New Mexico  and described February 23, 2017.  Although not in my collection, karpenkoite [Co₃V₂O₇(OH)₂—2H₂O] is the cobalt analogue of volborthite since cobalt substitutes for the copper.  Martyite is the zinc analogue when zinc replaces the copper [Zn₃V₂O₇(OH)₂—2H₂O]. Engelhauptite has the water (H₂O) molecules replaced by potassium and chlorine molecules [KCu₃(V₂O₇)(OH)₂Cl].

 

In summary (finally), vanadium is not well recognized by most non-rockhounds and is rarely found in nature; however, it is the 20^th most common element in rocks of the earth’s crust and is about as common as copper.  The interesting “thing” about vanadium, at least to a mineralogist, is that it forms a large community of anions (vanadium plus oxygen) that is turn are important components of a variety of minerals. I tried to describe some of these minerals in several postings listed above.

There is no end to education. It is not that you read a book, pass an examination, and finish with education. The whole of life, from the moment you are born to the moment you die, is a process of learning.     Jiddu Krishnamurti  

And believe me, I have learned much about vanadium minerals!!!  WOW.

REFERENCES CITED

Evans, H.T., Jr., R.M. Garrels, 1958, Thermodynamic equilibria of vanadium in aqueous systems as applied to the interpretation of the Colorado Plateau ore deposits: Geochimica et Cosmochimica Acta, v. 15, nos. 1-2.

Evans, Jr., H.T. G.N. Nord, J.M. Marinenko and C. Milton, 1984, Straczekite, a New Calcium Barium Potassium Vanadate Mineral from Wilson Springs, Arkansas:
Mineralogical Magazine, v. 48.

Foshag, W.F., F. L. Hess, 1928, Rossite and metarossite; two new vanadates from Colorado: Proceedings of the U.S. National Museum, v.72, no. 1.

Hollingsworth, J. S.,1967, Geology of the Wilson Springs Vanadium Deposits: Geological Society of America, Central Arkansas Field Conference Guidebook, v. 22, no.8.

 

Howell, K.K., A history of the mines at Tiger, Chapter 7, 1991, In History of Mining in Arizona, Volume II, J.M. Canty and M.N. Greeley, eds.: Mining Club of the Southwest Foundation, Tucson, Arizona.

 

Millman, A.P., 1960, The descloizite-mottramite series of vanadates from Minas do Lueca, Angola:The American Mineralogist, v. 45.

Ostrooumov, M., and Y. Taran,  2015, Discovery of native vanadium, a new mineral from the Colima Volcano, State of Colima (Mexico): Revista de la Sociedad Española de Mineralogía, v. 20.  

D.J. Strumfels, A medley of potpourri.blogspot.com/2019/06/vanadium.html.

Zhang, L., Z. Shi, G. Yang, X. Chen, S. Feng, 2000, Hydrothermal synthesis and crystal structure of a layered vanadium oxide with an interlayer metal co-ordination complex: Cd[C₃N₂H₁₁]₂[V₈O₂₀]: Journal of the Chemical Society, Dalton Transactions, Issue 3.