Gypsum

Gypsum

Gypsum, Calcium sulphate dihydrate, CaSO4 . 2H2O  is an evaporite mineral.  The variety of this specimen is known as selenite, and it probably derives it's deep green colour because of the locality of its origin, which is the Lubin copper mine in Poland. Gypsum is very variable in colour and habit, and crystals can vary in size from a few millimetres to several metres, dependent on depositional conditions and proximity of other minerals. The conditions at Lubin have produced this instantly recognisable selenite variety of small green acicular crystals.