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Selenite Crystals are a variety of the mineral gypsum, showing an obvious crystalline structure. Gypsum, including selenite crystals are composed of calcium sulfate dihydrate with the chemical formula CaSO4•2H2O. Selenite contains no significant selenium; the similarity of names comes from both substances being named from the Ancient Greek word for the Moon. In dry, desert conditions and arid areas, sand may become trapped both on the inside and the outside of gypsum crystals as they form. Interior inclusion of sand can take on shapes such as, an interior hourglass shape common to selenite crystals of the ancient Great Salt Plains Lake bed, Oklahoma, USA., (descriptive textual content drawn from Wikipedia) Preceding photos courtesy of StateSysymolsUSA.org Preceding photo courtesy of Miami Valley Mineralogical Society Return to List Back to Michael's Hobbies page Back to Michael Marcotte's HomePage