VANADINITE: TUCSON GEM SHOW REPORTS: MAIN STREET

Google Earth © view of Canada del Oro and Sutherland Wash near Catalina State Park.

The annual Tucson Shows have begun. The Day 1 for many shows was on Saturday January 31, a day of rather rare desert precipitation in the city.  In fact, the Mt. Lemon area in the Santa Catalina Mountains (that dominate the Tucson skyline) received in excess of five inches of rain.  Several of the area rivers, normally rather dry in most years, were roaring and quite impressive.  Canada del Oro in Oro Valley near Catalina State Park, my temporary home, was booming and carrying a wide selection of sand, pebbles and cobbles.  Sutherland Wash, a tributary of Canada del Oro in the Park, actually pushed enough “sand” onto the only access road and closed the campground to visitors getting “in or out.”  It was great to observe such a massive desert winter storm and see associated erosional and depositional processes.

 

Sutherland Wash drains the bajadas coming off the western flank of the Catalina Mountains.  During times of high rain fall the Wash funnels (right to left) large amounts of “sand” toward the master stream, Canada del Oro (hidden to the left), and often deposits the sediment in and on the major road leading to the Park campgrounds.

I spent my first show day, on Monday, visiting the Arizona Mineral and Fossil Marketplace on north Oracle Street. Essentially, the show is the first cluster of tents as one drives south on Oracle toward the city center.  There are some small time “mom and pop” dealers in the tents and I am especially partial to a couple of them.  Both have a wide selection of moderately-priced (sometimes  cheap) minerals as well as some beautiful three figure specimens.  However, I am most interested in purchasing specimens to supplement my collection that are on the lower end of the price selection.  And, these small dealers are more than willing to indulge in conversation with “ordinary” citizens and rockhounds.

Rock Deco is a locally owned (Tucson) shop specializing in Arizona minerals at a reasonable price.

So, what was my best purchased specimens costing five bucks or less?  Today it is a hand specimen of vanadinite crystals scattered on a bed of calcite collected from the San Carlos Mine (Apex Mine) in San Carlos, Mun. de Manual Benavides, Chihuahua, Mexico.  I could not locate much geological information on the San Carlos area except Moore (2008) noted “the San Carlos replacement deposit of argentiferous galena, mined briefly in the late 19th century and again from ca. 1930 to 1952, has produced beautiful and distinctive vanadinite specimens, as well as a limited number of superb wulfenite specimens.”

Gemmy calcite matrix with scattered tan vanadinite crystals (largest is ~5 mm).  Width of bottom specimen ~12 cm.  Upper photo is a closer view.

The calcite matrix is rather gemmy and fluoresces a nice green color with my UV light.  The vanadinite crystals, intergrown in the calcite rhombs, are elongated and euhedral, up to 5 mm in length, are tan to tan-orange in color, and have the typical barrel shape in cross section.  One dealer told me that most specimens like this were mined during the 1970s and 1980s and very few have come out in the last 25 years.  

  

Photomicrograph of a ~4.5 mm vanadinite crystal. The cross sectional view shows the typical hexagonal shape.

Vanadinite is a lead chlorvanadate [Pb₅(VO₄)₃Cl] with hexagonal crystals, various hues of red to orange to brown in color, less than adamantine in luster, and soft at ~2.5-3.0 in hardness (Mohs).   It forms a solid solution with pyromorphite (lead chlorophosphate) and mimitite (lead chloroaresnate). MinDat notes it is a secondary mineral found in the “oxidation zone of lead deposits in arid climates resulting from the alteration of vanadiferous sulphides and silicates of the gangue and wall rocks.”  My question is: what sulfide (primary zone) in the Apex mine contains vanadinite?  The list of 17 minerals noted in MinDat does not list a sulfide that is obviously, at least to me, a “vanadiferous sulphide.”  Of course I am far from any sort of a petrologist.  

I found it interesting that Professor del Rio (School of Mines of Mexico) discovered the mineral vanadinite (brown lead) in 1801before Niles Sefstrom “discovered” the element vanadium in 1830.  Del Rio knew that his “brown lead” contained a new element which he named erythronium but later recanted his name.

So, the big event is off and running and I am excited for the chance to explore.

REFERENCES CITED

Moore, Thomas, 2008, Famous Mineral Localities: The Apex Mine, San Carlos, Chihuahua, Mexico. Mineralogical Record v. 39 no. 6.