VANADIUM MINERALS: LASALITE AND CORVUSITE

Tell me what thy lordly name is on the Night’s Plutonian shore!” Quoth the Raven “Nevermore.”

Vanadium minerals are some sort of an enigma to most rockhounds; however, most know about a lead vanadate named vanadinite but remain rather unfamiliar with other minerals.  I would also guess that most of us have a specimen or two of vanadinite in our collections since hexagonal (barrel shape) crystals are a beautiful, bright, red color and sort of light up any mineral display.

The element vanadium (V), however, rarely occurs au naturelle and usually bonds with other elements, especially oxygen (O).  One of the common bonds is where 4 oxygen ions (each with a oxidation charge of 2 minus) combine with a single vanadium ion (oxidation charge of 5 plus) to form a vanadate ion in the form of a tetrahedron. Since the oxygen has a total of 8 minus, the oxidation charge of the vanadate ion, VO₄, is a 2 minus.  This particular ion with a negative charge always acts as an anion and commonly bonds with a positively charged metal or semi-metal (the cation).  Recently I posted a story (Oct. 15, 2019) about the mineral pucherite where the vanadate ion (anion) combines with the cation bismuth (BiVO₄).  Further back in the Blog archives is a posting (Feb. 6, 2017) on pottsite a hydrated lead bismuth vanadate [Pb₃Bi)Bi(VO₄)₄-H₂O] and vanadinite (Feb. 4, 2015) a lead chlorovanadate [Pb₅(VO₄)₃Cl].  However, vanadium also occurs in minerals where it acts as a cation with a 5 plus (usually) oxidation charge, V+++++.  One such mineral in this group is volborthite, a hydrated copper vanadium hydroxide [Cu₃V₂O₇(OH)₂—2H₂O].  My Posting on this mineral is on February 23, 2017.  All of these noted vanadium minerals are found in the oxidized zones of polymetallic mines where there is some sort of a primary vanadium source mineral.

The vanadate ion (VO₄) with a 3 minus oxidation state: 4 oxygen atoms surrounding a central vanadium atom in a tetrahedron.  Each oxygen has a 2 minus oxidation state while the vanadium is a 5 plus.  So, 8 - 5= 3 minus.  Diagram modified from Physical Geology, Opentextbc.ca.

Several decades ago I, along with my fossil collecting buddy, were out in western Colorado/eastern Utah with a group of paleontologists/geologists examining Mesozoic rocks for vertebrate fossils (yes we had permits).  On the drive back to Salt Lake City we had some time to kill and decided to check outcrops of the Jurassic Morrison Formation that were numerous south of the La Sal Mountains.  We also noticed dump piles from abandoned uranium mines scattered across the countryside that were remains of the massive Colorado Plateau uranium boom in the in the 1940s- 1960s.  I really don’t mess with uranium minerals such as carnotite (actually a uranium oxide with the vanadate ion) since I don’t want my office/collection to glow.  Generally, if a Colorado Plateau mineral is yellow or perhaps green I simply leave it alone.  However, on this trip I saw a really bright yellow substance on a pebble and picked it up to examine.  A geologist with the group told me it was a vanadium mineral rather than carnotite, so I brought it home where it resided for a number of years noted as a “vanadium mineral.”  At a later date I asked a mineralogist familiar with Plateau minerals to take a peek and his answer was lasalite, probably from the Vanadium Queen Mine—good enough for me.

As one could guess from the name, the mineral was given its moniker from the location around the massive La Sal Laccolith (see Posting Jan. 22, 2014) located south of Moab, Utah, and the high mountains that visitors to Arches National Park always notice (hey ranger, are those the Rocky Mountains?).  There are a number of named mining districts in this part of the Colorado Plateau with uranium and copper being the major metal targets (see Posting Feb. 19, 2012), and blueberry azurite being a mineral of rockhound interest (see Posting  Jan. 22, 2014).  Each of these districts has a large number of named mines, and of unnamed prospects.  The specimen I have came from one of those dumps and I will just go with the Vanadium Queen Mine. 

Lasalite is an interesting mineral for several reasons, not the least of which is the chemical formula: Na₂Mg₂(V₁₀O₂₈)—20H₂O.  Most vanadium minerals I yak about in posts are vanadates where 4 oxygen ions surround a central vanadium ion in a tetrahedron.  Lasalite starts out with 6 oxygen ions surrounding a central vanadium ion in an octahedron with edge and corner sharing of oxygen ions and ends up with a decavanadate ion (10 [deca] octahedra joined together in a single ion] with an oxidation state (charge) of 6- [let me explain that my chemistry is pretty suspect and I spent hours working on little tidbit].  In lasalite the cations are two sodium atoms (oxidation number of 1+ and two magnesium atoms (oxidation number of 2+.  So, 2 x 1=2 and 2 x 2=4 therefore 2 + 4 equals 6+, the same as the 6- in the decavanadate anion and, and therefore "everything balances balances (I am trying to "relearn" chemistry).

The decavanadate ion (V₁₀O₂₈) with a 6 minus oxidation state: 28 oxygen ions with 10 vanadium ions.  Each oxygen in a 2 minus while the vanadium is in the 5 plus oxidation state. So, 56 - 50 = 6 minus.  Diagram courtesy of Hughes and others (2005).  

Another reason for interest is that lasalite forms as an efflorescence (water in the matrix reaches the surface and evaporates leaving behind mineral residue) oxidizing on mine walls and fractures in the sandstone matrix (usually the Jurassic Morrison Sandstone in the Colorado Plateau.  The primary source of the vanadium is usually the mineral corvusite, a vanadium oxide (more later on this mineral).

In the Colorado Plateau Type deposits, a sandstone-hosted mineral deposit, vanadium minerals often occur with uranium minerals; therefore, rockhounds originally believed yellow vanadium minerals such as volborthite were radioactive; however, the Geiger Counter readings were just the radioactivity coming off accompanying uranium minerals. But, vanadium is a critical component of some uranium minerals such as carnotite: K₂(UO₂)₂(VO₄)₂--3H₂O.
 
And finally, MinDat.org notes that lasalite is identical in all respects to pascoite and other members of the Pascoite Group and can only be distinguished by X-ray diffraction or chemical methods.  Members of the Group, huemulite, hummwrite. magnesiopascoite, pascoite, rakovanite, differ in the amount of sodium, magnesium, calcium and potassium as cations combined with the V₁₀O₂₈ anion.

A yellow efflorescence of lasalite with corvusite in upper right corner.  Width FOV ~1.3 cm.

Photomicrograph showing submillineter crystal of prismatic lasalite,  Width FOV ~ 5 mm.

Lasalite has that very distinctive (like many vanadium minerals) yellow to yellow-orange color with a yellow streak.  The individual crystals are extremely small but if individuals are located they tend to be prismatic or blocky or even rounded, and glassy to silky in luster.  It is extremely soft at ~1.0 (Mohs).  Crystals are very brittle and can dehydrate to a yellow 

powder.  And, the crystals look very similar, if not identical to, other members of the Pascoite Group!

The Vanadium Queen Mine, situated on La Sal Creek Canyon, was originally staked in 1931 and went through a number of owners until being acquired by the Vanadium Queen Mining Corporation in 1955 during the “heyday” of uranium mining in the Colorado Plateau.  The ore body was a channel sandstone in the Jurassic Salt Wash Sandstone Member of the Morrison Formation.  My advisor at the University of Utah (late 1960s) once worked for the Atomic Energy Commission prospecting for uranium ore (carnotite, uraninite, tyuyamunite, metatyuyamunite, etc.) and told students that was secret for finding rich ore in the channel deposits was to locate the inside of meanders in the paleochannels.  In these inside bends plant debris carried in the stream often was deposited (trash pockets) and the carbon-rich material then provided a reducing environment for vanadium and uranium ions carried in ground water and ore bodies were created by replacement of the carbonaceous material, filling of pore spaces between sand grains, and coating of individual detridal grains.

I could not locate specific production figures for the Vanadium Queen; however, Carter and Gualtieri (1965) noted “the La Sal Creek mining district lies on the Colorado border about 30 mi southeast of Moab in San Juan County. The district is a significant V-U producer and ranks as the fourth largest V producer in Utah. Total district metal production at modern metal prices is estimated at $63 million. The major mines are the Firefly, Vanadium Queen, and Black Hat underground mines. The Vanadium Queen is one of the largest and highest grade V mines in the state at over 2% V2O5.” According to the Utah Geological Survey uranium-vanadium production in the La Sal Creek District lasted from 1904-1973 with a total dollar ore value of around 62.5 million dollars.

The source for the secondary vanadium minerals (such as lasalite ) at the Vanadium Queen Mine, and probably at many/most other Morrison Formation vanadium mines, is corvusite, a nondescript hydrated sodium, calcium, potassium, magnesium, vanadium oxide (and pretty ugly): (Na,K,Ca,Mg)₂(V⁵⁺V⁴⁺Fe²⁺)₈O₂₀--6-10H₂O. Note there are actually two

vanadium ions in the mineral, V+++++ and V++++.  In addition, the iron is ferrous iron the Fe++ oxidation state (as opposed to ferric iron, Fe+++).  

Corvusite is tough to identify except to realize that a blue-back to black to brown, opaque mineral in the sandstone matrix might be the vanadium oxide mineral (or it might be a uranium mineral!).  The specimens I have seen seem to have that distinctive blue-black color, but a color tough to pick up on my digital camera.  Most corvusite has a massive habit; however, some specimens show fibrous crystals.  All have a very dull to earthy luster and are soft at 2.5-3.0 (Mohs).

Black corvusite grains/crystals.  Width FOV, top ~6 mm, bottom ~7 mm.

The Firefly-Pigmay Mine, a uranium-vanadium deposit, is located near the Vanadium Queen Mine and has the same type of geology.  My specimen of corvusite was collected at this mine. 

The exact source of the original vanadium in these deposits is somewhat uncertain; however, Thamn, Kovschak and Adams (1981) noted the “Salt Wash 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.”

REFERENCES CITED

Carter, W.D., and Gualtieri, J.L., 1965, Geology and uranium deposits of the La Sal quadrangle, San Juan County, Utah, and Montrose County, Colorado: U.S. Geological Survey Professional Paper 508, 82 p., 13 plates.

Hughes, J.M., Schinder, M., Francis, C.A., 2005, The C2/m disordered structure of Pascoite, Ca₃[V₁₀O₂₈]-17H₂O): Bonding between structural units and interstitial complexes in compounds containing the [V₁₀O₂₈]₆-decavanadate polyanion: The Canadian Mineralogist, v. 43, pp. 1379-1386.

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.

Several decades ago, during my halcyon days of high school, every student that went through Miss Rees' English class needed to memorize a section of Edgar Allan Poe's poem The Raven.  All any student remember a few years later was Quoth the Raven, "Nevermore."

The avian genus Corvus was named by the biologist Linneaus in his opus magnum, Systema Naturae.  Linneaus named the Common Raven Corvus corex after the Latin name for raven while the specific name, corax, is the Ancient Creek name for raven.  The American Crow is Corvus brachyrnynches with the specific name Latin for short billed. 

Having for many days past confined myself to the boat, I determined to devote this day to amuse myself on shore with my gun and view the interior of the country lying between the river and the Corvus Creek—    accordingly before sunrise I set out with six of my best hunters, ^[1] two of whom I dispatched to the lower side of Corvus creek...one of the hunters killed a bird of the Corvus genus  and order of the pica & about the size of a jack-daw with a remarkable long tale. beautifully variagated.  From the Journals of Lewis and Clark, September 17, 2004.

This is the first description of the black-billed magpie in western North America.  They named Corvus Creek for magpie, one of the few times that Lewis used a Latin zoological term.  Sometime between 1804 and the present, the name for this creek north of Chamberlain, South Dakota, emptying into the Missouri. River was changed to Crow Creek. In addition, the magpie is no longer assigned to the genus Corvus but to Pica.

Corvus the Crow is a southern constellation between Virgo and Hydra.

In 1933 Henderson and Hess named a dark colored (black or blue-black or dark brown) mineral collected from the La Sal Mining District (Jack Claim) corvusite in allusion to its blue-black color similar to the color of a raven's feathers. 


Henderson, E.P. and F.L. Hess,1933: Corvusite and rilandite. new minerals from the Utah-Colorado carnotite region: American Mineralogist, v.18.