Gypsum CaSO4.2H20 (Hydrous Calcium Sulfate) is the commonest sulfate. It is a major rock forming mineral that forms massive beds, usually from precipitation out of highly saturated waters. Since it forms easily from saline water, gypsum may have many inclusions of other minerals and even trapped bubbles of air and water.

Description: Several crystal clear tabular crystals of gypsum are the centrepiece of this specimen. Closer examination shows that many of the crystals are actually composed of very thin overlying sheets. However the clarity means that this structure can only be seen from the side of the formations. Richly scattered around the surface of the matrix and lying below some of the gypsum are very shiny crystals of copper-coloured Marcasite. Many of these crystals have excellent orthorhombic habit and show marked irridescence.

Location: Lubin, Poland.