Translucent, bluish/grey, river-worn, nodule of chalcedony with numerous radiating inclusions of manganese oxide. Found in the Agate Flats area, north of the Sweetwater River, Freemont County, WY. Named after the Sweetwater River, Sweetwater agate shows a bright green fluorescent response under short wave UV due to the inclusion of trace amounts of uranium (in the form of the uranyl ion), which also causes this material to emit a low level of radioactivity (~90 cpm). This specimen shows a less-bright green response under medium wave UV, and a dim green response under long wave UV. Sweetwater agate is also a popular lapidary material. This size of this agate nodule is 57 x 32 x 26 mm, and it weighs 49 grams.