Selenite and Satin Spar are both varieties of the mineral gypsum, but they differ in their crystal structure and appearance. Selenite typically forms in transparent, flat, and blade-like crystals, often appearing colorless or lightly colored. Satin Spar, on the other hand, is a fibrous form of gypsum, characterized by its milky white color, silky texture, and chatoyancy (a shimmering, cat's eye effect).
