(Jon of the Clue Crew holds a white rock at White Sands National Monument, New Mexico.)  Because it's water-soluble, this form of calcium sulfate is rarely found in sand, but here in New Mexico's Tularosa Basin, there are no rivers to carry it away, so it forms the famed white sand
The sands of White Sands National Monument are formed from ... it is rarely 
found as sand because it easily dissolves in water, and rivers ...