A mass of bladed crystals of a water-soluble salt (usually gypsum, sometimes barite or calcite) that precipitate out of evaporating groundwater in an arid environment. Sometimes resembling spiked balls, other times resembling roses, they are usually found in areas prone to evaporation and reflooding, such as the sabkhas of eastern Arabia or around playa lakes in the American Southwest.
Gypsum desert roses, when found in nature, are entirely brown. A desert rose whose crystals have white edges has been "enhanced" by a dealer with a propane torch.