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, Freemont County, WY. This agate is a regionally popular lapidary material, but it also shows a striking fluorescent response under UV. The bright green short wave UV response is uranyl-activated, confirmed by the presence of numerous uranium mines in the Freemont County area. The orange response seen under long wave UV may be Mn-activated, as suggested by the presence of the manganese oxide dendritic inclusions. This size of this agate nodule is 54 x 40 x 26 mm, and it weighs 67 grams.