gismondine

gismondine, rare mineral in the zeolite family. Many specimens have been found in Ireland and Iceland in basaltic lavas, along with such other zeolites as chabazite, thomsonite, and phillipsite. Gismondine forms colourless, bipyramidal crystals of orthorhombic symmetry; it is a hydrated calcium aluminosilicate with the formula Ca₂Al₄Si₄O₁₆·9H₂O.