sulfates
Gypsum
Ca(SO4)·2H2O
- Also known as
- selenitesatin sparalabasterdesert rose
- Crystal system
- monoclinic
- Hardness
- 2 on the Mohs scale
- Lustre
- vitreous
- Colour
- Colourless, white, grey, occasionally amber
- Where it forms
- By evaporation of seawater or saline lakes. Thick gypsum beds mark places where an ancient sea dried up.
- Chiefly from
- Naica, Chihuahua, MexicoMoroccoSpainNew Mexico, United States
Why it is that colour
Pure gypsum is colourless or white; clay and iron give the browns and greys.
Safety
Safe to handle. It is soft enough to scratch with a fingernail and it is soluble in water — a gypsum piece left in water will visibly degrade. This is the practical reason not to wash it, quite apart from the general rule about stones and drinking water.
Where it comes from
Abundant and quarried in enormous quantity — gypsum is plasterboard, plaster of Paris and a component of cement. Moroccan material supplies most of the wellbeing market.
Historical use
Heated, it loses most of its water and becomes plaster of Paris, which sets hard again when mixed with water. That reaction has been used since at least ancient Egypt, and it is the basis of plasterwork, casts and modern plasterboard.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Alabaster has a long history as a carving material, but gypsum in its own right carries no significant traditional symbolism. The name selenite comes from the Greek for moon, applied because of its pearly sheen. The modern reputation for cleansing and clearing is New Age.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Worth knowing
The Cave of the Crystals at Naica in Mexico contains the largest natural crystals ever found: gypsum beams up to eleven metres long and weighing tens of tonnes. They grew over perhaps half a million years in water held at just under sixty degrees, almost exactly at the temperature where anhydrite converts to gypsum, so growth was extraordinarily slow and uninterrupted.
The cave is only accessible because mine pumping lowered the water table, conditions inside are lethal within minutes without equipment, and the crystals began to degrade once exposed to air. The mine has since been allowed to reflood, which is probably the best thing for them.
Identity checked against IMA-CNMNC master list, June 2025.