Selenite.

Selenite is the translucent fibrous form of gypsum, a hydrated calcium sulphate soft enough to scratch with a fingernail. The name comes from the Greek selene, moon, for the soft pearly sheen the stone takes when polished. The Naica caves in Mexico produced the famous giant selenite crystals, some over ten metres long, formed in mineral-rich water at near-perfect saturation conditions over hundreds of thousands of years.

Across modern crystal practice selenite has settled into a particular role: it is the stone people keep on the shelf to clear and reset other pieces. Place an amethyst point or a tumbled rose quartz on a selenite plate overnight and the tradition holds that the working stone returns to a quiet baseline. Whether or not one takes the symbolic claim literally, the practice is gentle, takes up little space, and gives a piece a regular ritual of attention.

The one rule with selenite is that it must stay dry. Gypsum is mildly water soluble, and a glass of water on a selenite plate will fog and pit it within minutes. Skin contact is fine in moderation, but storing selenite in a bathroom or anywhere with consistent humidity will slowly degrade it. With dry handling and out of direct moisture a selenite plate keeps its quiet glow for years, soft enough to read in low light and present without making any particular demand.