This is the mineral Gypsum. Gypsum belongs to the Sulfate chemical family. Sulfate minerals contain a Sulfate ion. Sulfate ions are tetrahedral shaped compounds consisting of a central Sulfur atom surrounded by 4 Oxygen atoms. It often exhibits a vitreous, or glassy, luster, but some specimens display pearly or dull lusters. For example, the crystalline variety of Gypsum called Selenite has a pearly and even silky luster, while Gypsum’s massive variety often exhibits a dull luster. It has a white streak and a specific gravity of about 2.3. Gypsum is a very soft mineral that defines hardness rank number 2 on Mohs hardness scale. Thus, Gypsum can only scratch Talc, which is ranked number 1. Gyspusm exhibits good one directional cleavage, resulting in thin, rectangular fragments, but this often depends on the Gypsum variety. This mineral has been used throughout much of human history. It’s the primary ingredient in plaster, and thus extensively used in construction. Plaster is used to smoothly coat walls or decorate ceilings. It’s applied wet and then hardens as its water content evaporates. The term Plaster of Paris is derived from the Gypsum deposits mined from the Paris Basin. This Gypsum is heated to drive off its water content, thereby creating the mineral Anhydrite. Anhydrite has the same chemical composition as Gypsum, except for Gypsum’s water content. When water is mixed into powdered Anhydrite, it becomes the malleable paste that we call plaster. While artisans often use plaster to create decorative shapes and ornate ceilings, most homes and workplaces use a more prosaic form of Gypsum called drywall. You may know it as the trademarked name Sheetrock. The name Sheetrock is owned by the United States Gypsum Company, which creates this incredibly versatile building material. When not used in construction, Gypsum is sometimes used to enhance the Calcium and Sulfur content of soil. It’s also useful to slow the hardening of cement into concrete.