Gismondine is a mineral with the chemical formula CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>÷4H<sub>2</sub>O. It is a zeolite or hydrated aluminosilicate. It forms colorless, bipyramidal crystals of orthorhombic symmetry.
Gismondine was named for Italian mineralogist Carlo Giuseppe Gismondi (1762âÂÂ1824). It has been found in Iceland, Ireland, and Italy.