What Is Selenite? A Stone That Dissolves in Water

Selenite is a crystal form of gypsum (calcium sulfate), and it's genuinely soft — about 2 on the Mohs hardness scale, meaning it can sometimes be scratched with a fingernail. It's also water-soluble: prolonged contact with water can dull its surface or, over enough time, dissolve it. If you keep a selenite tower or plate at home, a dry cloth is the safer way to clean it rather than rinsing it.

Its name comes from the Greek word for "moon," a reference to the pearly, gently glowing sheen along its cleavage planes. The most famous selenite deposit is Mexico's Naica Mine, home to natural selenite crystals reaching several meters long; Morocco is another major commercial source.