Selenite is a varietal name of Gypsum, which is one of the more common minerals in sedimentary environments. It's primarily composed of Hydrated CalciumSulphate , it forms when limestone is attacked by sulphuric acid. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Gypsum has several variety names that are widely used in the mineral trade. "Selenite" is the colorless and transparent variety that shows a pearl like luster and has been described as having a moon like glow. Another variety is a compact fibrous aggregate called "satin spar" This variety has a very satin like look that gives a play of light up and down the fibrous crystals. This selenite massage/palm stone is nice and clear, it fits great in the palm of the hand. They are ideal for massaging over clothes.