Selenite [pronounced: sel·e·nite | \ˈse-lə-ˌnīt\] (CaSO4 2H20, Hydrous Calcium Sulfate or Calcium Sulfate Dihydrate) is a variety of Gypsum. Gypsum is one of the most common sulfate minerals found in the Earth’s rocks. Gypsum is formed from the crystallisation of evaporated ancient sea beds, lakes and hot water springs.
Selenite’s hardness on the Mohs scale is 2, its lustre is vitreous or pearly, its streak is white, and its system is monoclinic. Selenite forms in crystals which can be tabular (many-sided), bladed (fanlike), or blocky (cubic). It is typically colourless, but sometimes contains pale tints due to inclusions. If impurities are present, gypsum may also appear to be red, brown, greenish or yellow. Impurities are other mineral inclusions such as, copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite, and opal. Selenites can also occur in geodes alongside Quartz. Some specimens can be fluorescent or phosph