Selenite crystals at Lake Lucero.
Lake Lucero is contained within the White Sands National Monument in New Mexico. The lake is noted for the unusually high quantity of water-deposited and wind deposited gypsum dissolved in its intermittent waters. Annual evaporation cycles have caused much of the gypsum to precipitate into crystals of impure, brownish selenite that line the alkaline mudflats of the lakeshore. The further process of gypsum erosion abrades the fragile selenite, and other precipitated gypsum, into the pure-white sands covering most of the national monument.