Chameleon Agate from the Granite Mountains, Wyoming
Contributed by: Chris Clemens
minID: A5J-T1G
Date: Apr 23rd, 2026
Locality: Granite Mountains, Fremont County, Wyoming, USA (See on Mindat)
Size: 28 x 25 x 39 mm
Weight: 33 g
Description:
Agate/chalcedony nodule from the Granite Mountains, Fremont County, Wyoming, that shows a unique multi-colored fluorescent response dependent on the UV wavelength of excitation. Under shortwave UV (254nm) a bright green response is seen. A less bright green response occurs under midwave UV (305nm). Things get interesting under longwave UV (365nm) however, as this material fluoresces a beautiful peach/pink color. There are numerous uranium mines in the area where this material occurs, providing confirmation that uranium is the activator responsible for the green fluorescence seen under shortwave and midwave UV. However, a second activator appears to be at work under longwave UV to produce the pastel orange/pink response; possibly manganese and lead.
Originally posted by Chris Clemens on Nature's Rainbows in 2016.
Summary of luminescence responses:
Chalcedony (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Orange
- Fluorescence under Midwave (305nm Lamp/Mercury) UV light: Green
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green