Fresnoite: Unusual Titanium Coordination

Abstract

The crystal structure of fresnoite, Ba(2)(TiO)[Si(2)O(7)], consists of [Si(2)O(7)](6-) double groups and titanium-centered square pyramids linked to form flat sheets. Intercalated between these sheets are Ba(2+) ions in highly distorted pentagonal antiprisms. The structure of fresnoite is related to that of melilite, (Ca,Na)(2)(Mg,Al[Si(2)(7)].