An orthorhombic mineral, Na₂Ca₅Al₁₂Si₂₀O₆₄.27H₂O ; zeolite group; pseudotetragonal; forms radiating aggregates in amygdules in basalts, commonly associated with other zeolites, e.g., chabazite, thomsonite, and levyne; at the Garron Plateau, County Antrim, Ireland, and 22 localities in eastern Iceland.