Selenite – Crystal Wiki
Clear to silky – the translucent variety of gypsum
Gypsum / Selenite (CaSO4·2H2O)
Properties & Characteristics
Scientific Data
- Chemical Formula
- CaSO4·2H2O
- Crystal System
- Monoclinic
- Mohs Hardness
- 2
- Density
- 2.3 g/cm3
Physical Properties
- Color
- Colorless, white, cream
- Luster
- Vitreous to silky luster
- Transparency
- Transparent to translucent
- Special Feature
- Very soft and sensitive to moisture
What is Selenite?
Selenite is the clear to translucent form of gypsum. It is visually serene and is often used as a decorative and collectible mineral.
Formation
Selenite typically forms in evaporitic deposits from calcium and sulfate-rich solutions (evaporation lakes). A special phenomenon is extremely rapid, so-called fishbone habit growth under strong evaporation, which sometimes leads to massive inclusions.
Deposits & Market
Known occurrences include Morocco (mostly clear to white specimens), Mexico (two-meter long crystals from the Naica Mine), and Spain. The latter – particularly from Villarroya in La Rioja and Montalbán in Aragon – are famous for their exceptional black inclusions.
Special Features: The Raven Feather Phantoms
Spanish selenite crystals from the Cretaceous period often contain so-called 'raven feather' phantoms. These striking black patterns within the crystal formed from the rapid encapsulation of organic material, coal, black clay, tiny pyrite crystals, and hydrocarbons in an oxygen-poor lake.
Similar to tree rings, each of these black layers records changes in the environmental climate at the time – such as rainy periods, drought cycles, or sediment washed ashore by storms. For geologists, they are now an important climate archive; for collectors, fascinating witnesses to Earth's history. Read more about Spanish raven feather selenite →
Quality Characteristics
Important criteria are clarity, undamaged edges, and harmonious shape development. For specimens with phantoms, the contrast of the inclusions is crucial.
Care & Handling
Clean only dry or with minimal moisture; absolutely avoid prolonged water contact.
Frequently Asked Questions
Can selenite be cleaned with water?
Only briefly and very carefully. Permanent moisture harms the material.
Is selenite robust?
No, with a Mohs hardness of 2, selenite is very soft and susceptible to scratches.
Is selenite suitable for everyday jewelry?
Rather not; it is significantly more suitable as a collector's item.