Andersonite from Utah
Contributed by: Michael Crawford
Date: Jun 25th, 2025
Locality: Little Eva Mine, Yellow Cat Mesa, Thompsons Mining District, Grand County, Utah, USA (See on Mindat)
Size: 10 x 11 cm
Description:
This is a sandstone with yellow andersonite (Na2Ca(UO2)(CO3)3 · 6H2O) from the Little Eva Mine, Yellow Cat Mesa, Grand County, Utah. The specimen fluoresces blue-green under all wavelengths of UV light. The blue-green fluorescence is like other uranyl-carbonate minerals activated by the linear uranyl ion. They all have vibronic spectral peaks that are shifted to shorter wavelengths compared to the uranium minerals like autunite that fluoresce yellow-green (see spectral plots).
These are some other uranyl-carbonate minerals with blue-green fluorescence.
Schrockingerite (NaCa3(UO2)(CO3)3(SO4)F · 10H2O)
Bayleyite (Mg2(UO2)(CO3)3 · 18H2O)
Andersonite (Na2Ca(UO2)(CO3)3 · 6H2O)
Liebigite (Ca2(UO2)(CO3)3 · 11H2O)
The emission spectra of these minerals show that wavelengths of the vibronic peaks are slightly different from one another. The shifts are caused by differences in coordination between different cations, anions, and the uranyl ion in each mineral. Emission spectra have the potential to assist in the identification of uranium minerals.
The specimen’s radioactivity is around 1800 CPM.
Summary of luminescence responses:
Andersonite
- Fluorescence under Longwave (365nm LED) UV light: Green
- Fluorescence under Midwave (305nm LED) UV light: Green
- Fluorescence under Shortwave (255nm LED) UV light: Green