Photo: tsaiproject, Sunset (Some rights reserved) Wikipedia: Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4ยท2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard/sidewalk chalk, and drywall. New MexicoConditions of the White Sands National Park … Continue reading Gypsum