Gypsum

La description

  Physical properties

Gypsum is moderately water-soluble (~2.0–2.5 g/L at *5 °C)[6] and, in contrast to most other salts, it exhibits a retrograde solubility, becoming less soluble at higher temperatures. When the crystal lattice is heated it loses liquid water molecules to evaporation and thus gains solidity. As for anhydrite, its solubility in saline solutions and in brines is also strongly dependent on NaCl concentration.[6]

Gypsum crystals are found to contain anion water and hydrogen bonding.[7]

The word gypsum is derived from the Greek word γύψος gypsos, "chalk" or "plaster".[4] Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris.

Gypsum was known in Old English as spærstān, spear stone, referring to its crystalline projections. (Thus, the word spar in mineralogy is by way of comparison to gypsum, referring to any non-ore mineral or crystal that forms in spearlike projections.) In the early nineteenth century it was regarded as an almost miraculous fertilizer. American farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called "Plaster War" of ***2.[5]