Selenite

Selenite is the transparent, crystalline variety of gypsum, a natural hydrous calcium sulfate mineral (CaSO₄·2H₂O); it contains no selenium. Mindat notes that the name is mostly synonymous with gypsum and has historically meant the transparent variety, as opposed to fibrous satin spar and fine-grained alabaster. White, silky material showing a cat's-eye band, such as the beads the Japanese retailer Pascle sells as selenite, matches the definition of satin spar gypsum rather than transparent selenite.