Ferrierite

The ferrierite group of orthorhombic minerals with highly variable cationic composition, (Na,K)₂Mg(Si,Al)₁₈O₃₆(OH)·9H₂O. Calcium and other ions are often also present. They are found in vitreous to pearly, often radiating, spherical aggregates of thin blade-shaped transparent to translucent crystals.