Selenite

Selenite is the colourless, transparent crystalline form of gypsum; chemically it is the same as gypsum (calcium sulfate and water). In crystal shops the name “selenite” is also used loosely for other kinds of gypsum: fibrous satin spar, desert roses and gypsum flowers. The largest natural crystals known are selenite.

Windows: Thin, mica-like sheets were once used in place of window glass. Ornaments: Crystal rods, clusters and carved pieces are sold as ornaments; being soft, it is easily worked and easily damaged. Collecting: Large, transparent and twinned crystals are sought by mineral collectors. Gypsum: The same mineral turns into plaster when heated and part of its water is driven off; the gypsum used for plaster, plasterboard and cement is the same substance as selenite (see Gypsum).

It has a hardness of 1.5–2 on the Mohs scale. It is soft enough to scratch with a fingernail. Its specific gravity is 2.31–2.33 g/cm³.

Its best-known localities: Naica, Chihuahua, Mexico; Pulpí, Almería, Spain; Salt Plains National Wildlife Refuge, Oklahoma, USA; Lake Lucero, White Sands, New Mexico, USA; Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico, USA.

It is colourless and transparent; it has a glassy lustre and a pearly sheen on cleavage faces. A fingernail scratches it (hardness 2). It has perfect cleavage in one direction: it splits into thin, bendable sheets that do not spring back. It does not fizz in acid, which separates it from the similar-looking calcite. Unlike quartz it is scratched easily. Satin spar: silky fibrous rods are often sold as “selenite”, but selenite is transparent, crystalline gypsum, and the fibrous, silky kind is called satin spar. Both are gypsum.

On the “street to diamond” value ladder it sits on step 3 of nine: Building and industrial stone. Selenite is a common kind of gypsum; crystal rods, clusters and carved pieces are sold as ornaments. In collecting, the transparency and size of the crystal, the form of the twinning, freedom from damage and a famous origin such as Naica or Pulpí raise its value. Because it is so soft, scratches and breaks lower the value noticeably.

In ancient times selenite was believed to wax and wane with the moon; its name derives from the Greek selenites lithos, “moon stone”. Kunz reports that Mizauld, in the 16th century, described a white mark on a “selenite or moonstone” that grew and shrank with the phases of the moon. Today crystal-therapy practitioners claim that selenite cleanses the space it is in and the stones beside it of negative energy, and that it never needs “cleaning” because it cleans itself. Some news websites in Türkiye write that selenite clears energy blockages, brings abundance and blessing to the home, calms the mind and makes it easier to concentrate and sleep. The same articles claim selenite increases fertility and sexual desire and helps bone and skeletal problems, and even cysts. There is no scientific evidence that selenite cleanses a space, clears blockages of energy, or affects fertility, bones or cysts; problems with cysts, bones and fertility should be assessed by a doctor. It is not clear which mineral the “selenite or moonstone” Kunz mentions would be called today. Selenite dissolves slowly in water, so it should not be left soaking and “selenite water” should not be drunk. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.