Brightly Fluorescent and Radioactive Andersonite from Utah

Contributed by: Chris Clemens
minID: 3M3-W52
Date: Apr 23rd, 2026
Locality: D-Day No. 2 Mine, D-Day Mine group, Thompsons Mining District, Grand County, Utah, USA (See on Mindat)
Size: 3.8 x 1.3 x 4.3 cm

Description:
Brightly fluorescent andersonite with a minor metamunirite druse, from the D Day No.2 Mine, Yellow Cat District, Grand County, Utah. Andersonite is a rare secondary uranium carbonate mineral that forms as small bright to dull yellowish green colored translucent rhombohedral crystals, and as fine-grained drusy crystal aggregates. Being a uranium-containing mineral, andersonite is radioactive and is brightly fluorescent, showing a brilliant blue/green response under both shortwave and longwave UV, brightest under shortwave. The radioactivity of this specimen is approximately 1800 cpm at 1 cm.

Originally posted by Chris Clemens on Nature's Rainbows in 2016.

Fluorescence under shortwave UV light.

Fluorescence under longwave UV light.

Normal light.

Summary of luminescence responses:

Andersonite (Mindat) (RRUFF)

• Fluorescence under Longwave (365nm LED) UV light: Green
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green