Uranopilite from Utah
Contributed by: Michael Crawford
Date: Jul 21st, 2025
Locality: Widowmaker Mine, Fry Mesa, White Canyon Mining District, San Juan County, Utah, USA (See on Mindat)
Size: 7 x 10 cm
Description:
This specimen is from the Widowmaker Mine, White Canyon District, San Juan County, Utah. It contains two uranium minerals that fluoresce green under all wavelengths of UV illumination. One mineral is uranopilite ((UO2)6(SO4)O2(OH)6 · 14H2O) that is yellow in daylight. The other mineral is unidentified. It is pale green in daylight.
The shortwave emission spectra of the two minerals are very different. The uranopilite spectrum has two distinct peaks at 519 nm and 537 nm and an inflection around 565 nm. The spectrum of the unknown mineral has four distinct peaks at 498 nm, 520 nm, 543 nm, and 568 nm. The spectrum resembles the spectrum of saleeite, but saleeite is a uranium phosphate mineral. According to mindat, saleeite does not occur at the Widowmaker Mine. The other uranium minerals found at the Widowmaker Mine are all sulfates like uranopilite (bobcookite, johannite, magnesioleydetite, natrozippeite, plasilite, strassmannite). Emission spectra for these minerals are unavailable for comparison to the unknown mineral.
The radioactivity of this specimen is around 430 CPM.
Summary of luminescence responses:
Uranopilite (Mindat) (RRUFF)
- Fluorescence under Shortwave (255nm LED) UV light: Green
- Fluorescence under Midwave (305nm LED) UV light: Green
- Fluorescence under Longwave (365nm LED) UV light: Green