Quartz (Var: Chalcedony)
Bridgeport, Morrill County, Nebraska, USA
Chalcedony, pseudomorph after a gypsum "desert rose". These have been found in several counties in northwest Nebraska where the Chadron Formation outcrops. They fluoresce green (SW UV), as does most of the chalcedony from this area, because of trace amounts of uranium (as little as 1 ppm will create the fluorescence).
© Kelly Nash