Selenites

Selenite is a term used for two distinct topics: a mineral variety of gypsum and a fictional inhabitant of the Moon. The name comes from Selene, the Greek goddess of the Moon, reflecting the mineral’s pale, moonlike translucence and its place in mineralogical naming.

As a mineral, selenite refers to crystals of calcium sulfate dihydrate (CaSO4·2H2O). It forms through the evaporation of saline waters or hydrothermal processes and occurs in evaporite deposits, caves, and sedimentary environments. Selenite crystals are typically colorless to white and can be clear, transparent, or fibrous, often displaying a tabular habit. With a Mohs hardness of about 2, it is relatively soft and can be scratched easily. Notable large, clear crystals have been found in places such as the Naica Mine in Mexico. Selenite is used in the production of plaster and related materials, and cut or polished specimens are sought after by collectors and in decorative objects. The term is widely used in mineral circles to denote clear gypsum crystals.

In science fiction, selenites refer to imagined lunar inhabitants. The concept gained prominence after H. G. Wells popularized the term in The First Men in the Moon, where subterranean Selenites are depicted as an intelligent race living within the Moon. Since then, various works have employed the term with a range of physiologies and cultures, making selenites a longstanding archetype for moon-dwelling civilizations in fiction.