Mineral name: Gypsum
Chemical formula: CaSO4·2H2O
Physical properties: vitreous luster, hardness 2, white streak, Two directions of cleavage
Gypsum is used to make plaster, so mark any walls or ceilings that are plastered or made of sheet rock. It is also the main ingredient in the ceiling panels used in most classrooms and offices.
It is also used in making cement and concrete.
Most chalk board chalk is now made of gypsum.