ferrierite, hydrated aluminosilicate mineral, one of the members of the zeolite family present in sedimentary rocks. The chemical composition of ferrierite is approximately (Na,K)2MgAl3Si15O36(OH)ยท9H2O; it forms colourless, platy crystals of orthorhombic symmetry. The original specimen of the mineral was found in British Columbia; it is the principal constituent of an altered volcanic-ash deposit in central Nevada.