Golden Gypsum from Peru
Golden selenite gypsum, fish tail crystals clusters
Gypsum is made up of oxygen, sulfur, calcium and water. As evaporation occurs the sulfur is not protected by the water and oxygen contacts sulfur bonding with it to form a sulfate . The sulfate then bonds with calcium and water to create gypsum.
Gypsum forms whenever evaporation crystallizes the necessary minerals. In the case of "desert roses" gypsum crystals found around the world in arid sites, formation occurs with evaporation as the level of the water table changes.