Roscoelite

Description

Roscoelite has a hardness of 2½ and a specific gravity of 2.92 – 2.94. While it’s a little unclear when it was named and by whom, it’s named in honor of Sir Henry Enfield Roscoe, an English chemist particularly noted for early work on Vanadium and for photochemical studies, according to Mindat, and the first person to prepare pure Vanadium according to WebMineral.

According to Wikipedia, it “has been found in numerous places in US, Australia, Japan, Gabon, Fiji, New Guinea and Czech Republic. In the United States, it was the principal vanadium ore mineral at the mines at Placerville, Colorado. In Australia roscoelite has been found at Kalgoorlie, Radium Hill and the Kintore Open Cut at Broken Hill. Two kinds of mineral deposits contain roscoelite – either gold-silver-tellurium low temperature epithermal deposits where it occurs along with quartz, fluorite, pyrite and carbonates, or oxidized low temperature uranium-vanadium ores in sedimentary rocks, where it occurs with corvusite, hewettite, carnotite and tyuyamunite. Roecoelite is considered a gangue mineral of no value when found with gold, but it’s also been used as a vanadium ore. Roscoelite is a muscovite with aluminium substituted with vanadium. Vanadium can also be substituted by magnesium, iron, or manganese. The appearance is semi transparent to translucent colored olive brown to green brown. The lustre is pearly. The mineral shows pleochroism with X showing green-brown, and Y and Z axes showing olive-green color.”

Mostly comprised of Oxygen and Silicon at 46% and 20% respectively, Roscoelite is also around 10% Potassium, 10% Aluminum, and 10% Vanadium, with 2% Magnesium. While it’s not the primary ore for Aluminum or Potassium and doesn’t have as much Vanadium as Vanadinite, this mineral might just be the mineral from which the majority of all Vanadium was obtained, with as many mines as there are for this mineral as compared to many of the other Vanadium-bearing minerals, and would make for a great sample for element collectors!

There’s around 266 known recorded localities across the world for Roscoelite, with ~150 being on the Colorado Plateau – most being near Uravan and Placerville, Colorado. With it being found in two different types of environments, no matter where you are, be sure to keep an eye out for a rock like this on your next hike and you’ll not only be able to identify Roscoelite the next time you see it, but you might just also find your next Gold mine!