Gypsum has several variety names that are widely used in the mineral trade. "Selenite" is the colorless and transparent or translucent variety that shows a pearl like luster and has been described as having a moon like glow. The word selenite comes from the Greek for Moon and means moon rock. Another variety is a compact fibrous aggregate called "satin spar selenite." This variety has a very satin like look that gives a play of light up and down the fibrous crystals.