Stilbite

Formula: M6-7[Al8-9Si27-28O72] · nH2O where M = Na, Ca or K

Lustre: Vitreous, Pearly

Member of: Zeolite Group

Name: Named in 1797 by Jean Claude de la Métherie from Greek στιλβη “stilbein”, to glitter of shine, or “stilbe”, a mirror, alluding to its pearly or vitreous luster. Originally, but inconsistently called zeolite in 1756 by Axel Cronstedt. This name now refers to the zeolite subgroup including the Barrerite – Stilbite-Ca – Stilbite-Na – stellerite series. The end members barrerite and stellerite are orthorhombic and the others monoclinic, but the differences are subtle and difficult to pick by XRD and so the species need to be confirmed by a reliable chemical analysis. Crystals of this group are usually also chemically zoned. Prehnite and the Heulandite subgroup may also show a similar habit.