This is a larger specimen consisting of what appear to be two generations of calcite crystals on a limestone matrix, from the Linwood Mine, Buffalo, Scott County, Iowa. The earlier, first generation crystals cover the entire piece, and consist of small modified rhombs, most with marcasite inclusions. It is noteworthy that these crystals have a distinct amber to light brownish color. The later stage, second generation crystals, are much larger modified rhombohedrons, are colorless, and lie on top of the first generation crystals. Under short wave UV (254nm) the smaller first generation crystals fluoresce white, while the larger second generation crystals show a moderate to dim pink response. When the short wave lamp is turned off, the first generation crystals show a brief cream/white phosphorescent response. Under long wave UV (365nm) the first generation crystals again fluoresce white, but the larger second generation crystals are not significantly fluorescent. When the long wave source is discontinued, dim, brief, green phosphorescence is seen from the second generation crystals. As has been hypothesized in other posts of Linwood calcite on this site, these observations suggest that an organic activator is responsible for the white fluorescence of the first generation crystals, and an inorganic activator, such as manganese/lead, may be responsible for the pink fluorescence seen in the larger second generation crystals under short wave UV. The size of this specimen is approximately 7.0 x 5.5 x 3.5 inches.
Click on the individual images above for a larger view with wavelength information.