Selenite
Hydrous calcium sulfate (CaSO₄·2H₂O)
A clear, soft crystalline variety of gypsum that forms glassy or fibrous wands, so soft it can be scratched with a fingernail.
- Mohs hardness
- 2
- Color
- Colorless, white, translucent
- Type
- crystal
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Overview
Selenite is a clear to translucent crystalline variety of the mineral gypsum (hydrous calcium sulfate). It typically forms colorless, glassy crystals or fibrous, silky masses with a pearly sheen. Related gypsum forms include satin spar (the fibrous, light-reflecting variety often sold as selenite wands) and desert rose (rosette clusters with sand).
Selenite is remarkably soft—just 2 on the Mohs scale, so soft it can be scratched with a fingernail and scored with practice. It is also water-soluble, dissolving slowly in water, which makes it delicate to care for.
Its name comes from the Greek for moon, reflecting its soft, moonlight-like glow.
Formation & geology
Selenite forms by the evaporation of saline (sulfate-rich) water, precipitating gypsum in sedimentary basins, salt flats, sabkhas, and around hot springs. As mineral-laden water evaporates, calcium sulfate crystallizes out, sometimes growing into enormous crystals.
The most famous example is the Cave of the Crystals (Cueva de los Cristales) in Naica, Mexico, where stable hot, mineral-rich groundwater grew selenite beams up to 12 meters long over hundreds of thousands of years.
Gypsum is widespread; other notable selenite occurs in the USA, Morocco, and Madagascar.
How to identify it
- Hardness: Extremely soft at 2—a fingernail will scratch it. This nearly settles identification on its own.
- Cleavage: Perfect in one direction; it peels into thin flexible sheets or fibers.
- Luster: Vitreous to pearly; satin spar shows a silky chatoyant glow.
- Solubility: Slightly soluble in water (unlike calcite, which fizzes in acid).
Look-alikes: Clear quartz is far harder (7) and won't scratch with a nail. Calcite is harder (3) and fizzes in acid. The fingernail-scratch softness plus silky/glassy look is the giveaway.
Uses & significance
Selenite itself is mostly a collector and decorative crystal—carved into wands, towers, lamps, charging plates, and bookends—because it is too soft and water-sensitive for everyday jewelry.
The broader mineral, gypsum, is hugely important industrially: it is the raw material for plaster of Paris, drywall (gypsum board), and a cement additive, and is used in agriculture as a soil conditioner.
In metaphysical traditions selenite is associated with cleansing and clarity—cultural beliefs, not science. Keep it dry, as water will damage it.
Frequently asked questions
Can selenite get wet?
No—selenite is water-soluble and will become cloudy, pitted, or dissolve with prolonged moisture. Clean it only by dusting and keep it dry.
Is selenite the same as gypsum?
Selenite is a clear crystalline variety of the mineral gypsum. Satin spar and desert rose are other gypsum varieties often sold under the selenite name.
Why is selenite so easy to scratch?
At Mohs hardness 2, selenite is one of the softest display minerals—softer than a fingernail—so it scratches and chips very easily.
Is selenite safe to put in salt or water for cleansing?
No. Both salt water and plain water damage selenite. Cleanse it with dry methods like smoke or sound instead of liquids.
Selenite guides
In-depth guides for identifying, valuing, and understanding Selenite.
Selenite identified by the community
Real specimens identified with Rock Identifier.
