Sweetwater Agate, Agate Flats, Wyoming
Contributed by: Chris Clemens
minID: 80K-WUK
Date: Apr 24th, 2026
Locality: Fremont County, Wyoming, USA (See on Mindat)
Size: 40 x 26 x 54 mm
Weight: 67 g
Description:
This is a nodule of Sweetwater Agate, a translucent grey/blue dendritic agate found in the Agate Flats area, north of the Sweetwater River, near Jeffrey City, Fremont County, Wyoming. This agate is a regionally popular lapidary material, but it also shows a striking fluorescent response under UV. The bright green shortwave UV response is uranyl-activated, confirmed by the presence of numerous uranium mines in the Fremont County area. The orange response seen under longwave UV may be Mn-activated, as suggested by the presence of the manganese oxide dendritic inclusions.
Originally posted by Chris Clemens on Nature's Rainbows in 2016.
Summary of luminescence responses:
Chalcedony (Mindat) (RRUFF)
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green
- Fluorescence under Longwave (365nm LED) UV light: Orange