Gypsumia

Gypsumia is a hypothetical mineral proposed in theoretical mineralogy to illustrate the behavior of hydrated calcium sulfates. Named for its relation to gypsum, it is used in educational models to represent a family of calcium sulfate hydrates with variable water content depending on pressure and temperature.

In this model, gypsumia is described as a monoclinic phase with tabular crystals, colorless to white, and a vitreous luster. It is assigned a Mohs hardness of 2 to 3 and a specific gravity around 2.3 to 2.7. The concept envisions strong birefringence under polarized light and formation through evaporative precipitation in saline lakes or shallow seas, where it coexists with gypsum (CaSO4·2H2O), bassanite (CaSO4·0.5H2O), and anhydrite (CaSO4).

Gypsumia is treated as having a variable hydration state, with a chemical formula expressed as CaSO4·nH2O, where n ranges roughly from two to four under different conditions. Dehydration under drying or heating is thought to transform gypsumia into bassanite or anhydrite, while rehydration in humid environments can revert it toward gypsum-like compositions. This hydration-dehydration cycle makes gypsumia a useful theoretical example for studying phase transitions and crystal-chemical behavior in calcium sulfates.

In educational and research contexts, gypsumia serves as a conceptual tool to discuss hydration states, crystal chemistry, and evaporite geology. It has no confirmed natural occurrence in mineral databases and is not utilized in commercial applications, but it provides a framework for exploring how water content influences structure and stability in sulfate minerals.