Selenite

sulphates

2.2 to 2.4 g/cm3

unidirectional

excellent or good

CaSO4·2H2O

colourless or white

2 on the Mohs scale

pearl or glassy

Selenite crystals exhibit a variety of cross-sections, but the most common are tabular, prismatic or coniferous crystals, often without imperfections and inclusions, twin crystals are common and often found; occurs in combination with other minerals such as copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite, limestone and opal; it can be met most in North America and Europe; in Poland it may occur in the Nidy Valley, Lubinie, Dobrzyń on the Vistula River, Chodzieży near Piła

Selenite crystals can be very diverse in geometry, as this mineral has many varieties, which differ among other things in the structure of the crystals; it is a mineral from the group of sulfates; it is characterized by a pearly or glassy sheen, a shell fracture; it is excellent in one direction but good in both directions; it is used for the production of optical instruments, as collector's stones (especially those with a high degree of transparency) as a sculptural material

The name of this mineral comes from the ancient Greek words selḗnē (moon) and líthos (stone); it has always been called the "moonstone" because the light that passes through it has a characteristic soft glow; in the past it was used, among other things, to make glass, which fetched high prices; the largest crystal of this mineral was found in Mexico, in the Naica mine, it was 12 meters long and weighed 55 tons; is very susceptible to water in which it dissolves; ancient beliefs define selenite as the stone of the goddess Selena, the bright and angelic guardian of the Moon, who crosses the sky every night in her silver chariot; in ancient Rome, selenite was a valued mineral; Pliny the Elder emphasized the advantages of this mineral, which could be cut into thin layers through which light passed with a characteristic soft glow, similar to moonlight; sometimes, during the games held in the Circus Maximus, very fine selenite crystals were scattered on the sand of the arena to beautify the spectacle and add shine; pieces of selenite were also placed in road blocks as reflective elements, or "cat's eyes", as we call them today