sulfates
Selenite
Ca(SO4)·2H2O
- Crystal system
- monoclinic
- Hardness
- 2 on the Mohs scale
- Lustre
- vitreous
- Colour
- Colourless and transparent
- Where it forms
- As gypsum, from evaporating saline water, where conditions allowed large clear crystals to grow.
- Chiefly from
- Naica, MexicoUtah, United StatesMorocco
Why it is that colour
None — selenite is the clear, well-crystallised form of gypsum, and its interest is optical rather than chromatic.
Safety
Safe to handle, soft, and water-soluble. Do not wash it, do not leave it damp, and do not put it in water intended for drinking.
Where it comes from
Almost all commercial selenite is Moroccan, and almost all of it is satin spar rather than true selenite. See the entry for satin spar.
Historical use
Used for windows before glass was widespread — thin cleaved sheets of selenite are translucent, and Roman and medieval buildings used them as glazing. The word lapis specularis in Roman sources refers to this.
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
Named in the eighteenth century from Greek selene, moon, for its pearly reflections. That name is the whole of its lunar connection — there is no ancient tradition linking gypsum to the moon. Its modern reputation for cleansing other stones, and the accompanying claim that it never needs cleansing itself, dates from the New Age literature.
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.
Sold as this, but not
Worth knowing
Gypsum cleaves so perfectly in one direction that a crystal can be split with a fingernail into sheets thin enough to see through. The Romans used it as window glazing, quarrying it in Spain and shipping it across the empire; Pliny describes the trade. Fragments have been found in Pompeii.
That is a much better story than the one on the label, and it turns on the same property — perfect cleavage — that makes a selenite wand snap if you drop it.
Identity checked against IMA-CNMNC master list, June 2025.