Hübnerite

From Black Pine and Peru

Hübnerite is manganese tungstate, MnWO₄. To my eye it’s a “collector-friendly” mineral that often makes nice, bladed crystals, and it often has a distinctive reddish-brown color although it can be almost black.

The parallel growth crystals in the top photo are from the Black Pine Mine, Montana, famous for some of the best veszelyite (copper-zinc phosphate) crystals in the world, but also as home to at least 75 different mineral species, some of them pretty strange. Hübnerite isn’t especially strange but good specimens have come rarely from Black Pine.

The hübnerite in the top photo, just 9 mm high, sits on spindles of sharp quartz crystals on its back, but to me the interesting thing is the square crystal at left center, which is a bit less than a millimeter across. That’s stolzite, lead tungstate, Pb(WO₄), a fairly common associate of hübnerite especially in polymetallic deposits like Black Pine. For that crystal, the stolzite is a stubby tetragonal truncated pyramid, but often it forms more elongate tetragonal prisms such as in the photo below.

Field of view about 3 mm.  

Stolzite isn’t always fluorescent, but it often is. The crystal in the top photo fluoresces bright blue-white in short-wave (254 nm) UV light, but those in the second photo, above, fluoresce green, while the associated pyromorphite-mimetite in the small crystals at lower right fluoresces red-orange in long-wave (365 nm) light.

One might be tempted to infer from the blue-white fluorescence of the stolzite in the top photo that it could be scheelite, calcium tungstate. Scheelite is one of the few minerals that is intrinsically fluorescent (i.e., it always is because of its molecular structure, not because of impurities or defects). But calcium minerals in general are quite unusual at Black Pine and scheelite is questioned as to its presence at all. I think it is most likely by far that this crystal is stolzite.

Sometimes the hübnerite must have been crystallizing almost simultaneously with the quartz, as tiny blebs and crystals of hübnerite became included within quartz as it grew. Alternatively, the hübnerite may have been deposited on quartz crystal faces during a pause in quartz deposition. The quartz crystals above are about 41 mm in maximum height, and the included hübnerite crystals are fractions of a millimeter. I also used a symmetrical group of quartz crystals growing on a spear of hübnerite from Black Pine as my micro-mineral Christmas greeting last year.

One of the best-known localities for hübnerite is the Pasto Bueno District in Peru. There’s no Pasto Bueno Mine (which is shown on many labels); rather, the district includes several mines. According to MinDat it is usually impossible to assign a specimen to a particular mine. My specimen here is about 7 cm long, and the individual laths of hübnerite are about that long, associated intimately with lots of quartz crystals. There are also many tiny pyrite crystals on the hübnerite, mostly pyritohedrons smaller than a half millimeter across.

In some deposits, like Pasto Bueno, hübnerite is abundant enough to serve as an ore of tungsten, but wolframite and scheelite are the primary ores worldwide. Tungsten, mostly as tungsten carbide, is a vital component in cutting tools in the construction, mining, and oil and gas industries; modern civilization could not exist without tungsten. 80% of world tungsten production comes from China, which also holds more than 50% of the known reserves. The second largest producer in the world is Vietnam, with about 5% of the total. The United States has no commercial mine production of tungsten and reserves are tiny.

Because Americans don’t know what to do with umlauts, you sometimes see this mineral as huebnerite, or hubnerite without the umlaut. But it was named for Adolf Hübner, a German metallurgist from East Prussia (now Kaliningrad, Russia). The name given in 1865 by Eugene Riotte replaced the name megabasite, assigned by Breithaupt in 1852. Megabasite was given because Breithaupt thought (erroneously) that the mineral had more basic components (i.e., things that would react with acids, such as iron hydroxide) than wolframite, then construed as a mineral but now the group name for the series between hübnerite and ferberite (iron tungstate). Despite all these German connections, Riotte collected the original hübnerite specimens at the Ellsworth (Mammoth) Mining District in Nevada USA, the type locality. Riotte was Prussian-born but came to America as a child with his family in 1848; he was educated as a mining engineer and assayer at the Freiberg School of Mines in Germany, and worked in New York and elsewhere until his death in a mining accident in North Carolina in 1891 at age 48.

Stolzite honors Bohemian physician and mineral collector Johann Anton Stolz (1778 - 1855), who provided the first specimen of stolzite for study. Stolzite’s type locality is the Ore Mountains along the present-day border of Germany and the Czech Republic, between Prague and Dresden.

My Black Pine specimens here are from the collection of Bill Stanford, by way of Paul Senn.