Faujasite

Faujasite is a mineral group in the zeolite family of silicate minerals. The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula: (Na₂,Ca,Mg)_3.5[Al₇Si₁₇O₄₈]·32(H₂O) by varying the amounts of sodium, magnesium and calcium. It occurs as a rare mineral in several locations worldwide and is also synthesized industrially.

Discovery and occurrence

Faujasite was first described in 1842 for an occurrence in the Limberg Quarries, Sasbach, Kaiserstuhl, Baden-Württemberg, Germany. The sodium modifier faujasite(Na) was added following the discovery of the magnesium and calcium rich phases in the 1990s. It was named for Barthélemy Faujas de Saint-Fond (1741–1819), French geologist and volcanologist.

Faujasite occurs in vesicles within basalt and phonolite lava and tuff as an alteration or authigenic mineral. It occurs with other zeolites, olivine, augite and nepheline.

Structure

The faujasite framework consists of sodalite cages which are connected through hexagonal prisms. The pores are arranged perpendicular to each other. The pore, which is formed by a 12-membered ring, has a relatively large diameter of 7.4 Å. The inner cavity has a diameter of 12 Å and is surrounded by 10 sodalite cages. The unit cell is cubic; Pearson symbol cF576, symmetry Fd3m, No.227, lattice constant 24.7 Å. Zeolite Y has a void fraction of 48% and a Si/Al ratio of 2.43. It thermally decomposes at 793 °C.