Wiktionary
ettringite
n. (context mineral English) A trigonal hydrous calcium aluminium sulfate mineral.
Wikipedia
Ettringite
Ettringite is a hydrous calcium aluminium sulfate mineral with formula: CaAl(SO)(OH)ยท26HO. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of the ettringite-group which includes other sulfates such as thaumasite and bentorite.