Hexacelsian is a rare barium silicate mineral with the formula BaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>. It was discovered in the Hatrurim Basin in Israel, where the Hatrurim Formation of rocks formed due to exposed pyrometamorphism.
As suggested by its name, hexacelsian is related to celsian. This relation is polymorphous (celsian, a feldspar-group mineral, is monoclinic). Beside celsian, it is chemically similar to cymrite.