What is the difference between Gypsum and Anhydrite?

Gypsum, which is also referred to as hydrated calcium sulfate, and anhydrite, which is also referred to as hydrous calcium sulfate are both present in the sedimentary gypsum rock and anhydrite sedimentary rock respectively as their major minerals constituents. The constituents of gypsum are sulfur, calcium, and water, while the constituents of anhydrite are sulfur, calcium, and oxygen. Gypsum, which may occur as simple crystals, usually appears as twinned tabular crystals.

Gypsum is monoclinic, and it forms a fine granular masses or coarse sometimes. When impurities are present in gypsum, the color maybe orange, yellow, or brown, though it's usually white or colorless. Gypsum can be found in various parts of our localities, as it is common. Anhydrite does not react with hydrochloric acid, and they are orthorhombic. Anhydrites are hard crystals, and they are rated about 3.0 in density, and 3.5 in hardness. Anhydrites are scarce, and when they react with water after a long time, they will turn to gypsum.