laumontite, common hydrated calcium and sodium aluminosilicate mineral in the zeolite family, formulated CaAl2Si4O12·4H2O. Its white to yellow or gray prismatic crystals typically occur filling veins and vesicles in igneous rocks. It is one of the more abundant zeolites present in sedimentary rocks and is found, among other places, in Transylvania (Romania); in the Tirol, Austria; and in California, Oregon, and New Jersey, U.S. Its crystals have a framework structure of linked silicate and aluminate tetrahedra, water molecules, and large cations located within cavities. Cations such as calcium, sodium, and potassium readily replace one another in the structure, making laumontite useful in water softeners. For detailed physical properties, see zeolite (table).