Selenite is a transparent to translucent variety of gypsum, composed of calcium sulfate dihydrate (CaSO₄·2H₂O). It is known for its pearly, fibrous, or glass-like appearance and often forms in long, striated crystals or as large, sheet-like formations. Selenite is very soft, with a Mohs hardness of 2, making it easily scratched or carved. It is found in evaporite deposits, where water evaporation leaves behind mineral-rich layers. Major sources include Mexico, the United States, Morocco, and Greece. Selenite is commonly used for carvings, decorative pieces, and lapidary work due to its delicate beauty and natural luster.