The back side of this specimen reveals its origins. Radial gypsum crystals were deposited on a matrix mound (which disappeared later), followed by a generous coating of colorless, cubic halite crystals. The halites reach 5 mm and many are transparent and somewhat gemmy. Whitish fluorescence under both longwave UV (blacklight) and shortwave UV. Halite is often said to be unstable (hygroscopic) but this is generally due to impurities; pure halite is stable. (Regardless it is a wise precaution to store this specimen in a dry environment.) I have owned this sample for 15 years and it shows no signs of degradation. Excellent condition.