Gypsum...

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO₄·2H₂O.

Gypsum is used in a wide variety of applications:

Gypsum Board primarily used as a finish for walls and ceilings; known in construction as Drywall

• Plaster ingredient.
• Fertilizer and soil conditioner. In the late 18th and early 19th century, Nova Scotia gypsum, often referred to as plaster, was a highly sought fertilizer for wheat fields in the United States. It is also used in ameliorating sodic soils.
• A binder in fast-dry tennis court clay.
• Plaster of Paris (surgical splints; casting moulds; modeling).
• A wood substitute in the ancient world; for example, when wood became scarce due to deforestation on Bronze Age Crete, gypsum was employed in building construction at locations where wood was previously used.
• A tofu (soy bean curd) coagulant, making it ultimately a major source of dietary calcium, especially in Asian cultures which traditionally use few dairy products.
• Adding hardness to water used for homebrewing.
• A component of Portland cement used to prevent flash setting of concrete.
• Soil/water potential monitoring (soil moisture tension).
• A common ingredient in making mead.
• In the medieval period it was mixed, by scribes and illuminators, with lead carbonate (powdered white lead) to make gesso which was applied to illuminated letters and gilded with gold in illuminated manuscripts.
• In foot creams, shampoos and many other hair products.
• A medicinal agent in traditional Chinese medicine called Shi Gao.
• A medicinal agent in Ayurveda medicine's Rasashastra branch (Indian alchemy) (ref. Rasamruta).