This unusual fluorescent specimen consists of crystals of honey-brown selenite sandwiched between two layers of light grey chalcedony. This specimen is brightly fluorescent under mid wave UV, but only shows a weak response under short and long wave UV. This specimen was collected in the area of Hay Springs, Sheridan County, in northwest Nebraska. This specimen measures 15.6 x 8.6 x 5.1 cm, and weighs 670 grams.
The photograph above shows fluorescence under mid wave UV (302 nm). The selenite fluoresces a burnt orange color and the surrounding layers of chalcedony fluoresce bright green. The green fluorescence of the chalcedony layers is activated by trace amounts of uranium (in the form of the uranyl ion).
Under visible light above, honey-brown crystals of selenite are seen sandwiched between two layers of light grey chalcedony.