"Selenite, also known as satin spar, desert rose, or gypsum flower are four crystal structure varieties of the mineral gypsum. These four varieties of gypsum may be grouped together and called selenite.
All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate (meaning that it has two molecules of water), with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium, the similarity of the names of the substances coming from the Ancient Greek word for the Moon.
Some of the largest crystals ever found are of selenite, the largest specimen found in the Naica Mine´s Cave of the Crystals being 12 metres long and weighing 55 tons." - (en.wikipedia.org 09.03.2020)
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