title: Isokite, CaMg(PO(4))F(0.8)(OH)(0.2), isomorphous with titanite.
abstract: This study presents the first structural report of natural isokite (calcium magnesium phosphate fluoride), with the formula CaMg(PO(4))F(0.8)(OH)(0.2) (i.e. some substitution of OH for F), based on single-crystal X-ray diffraction data. Isokite belongs to the C2/c titanite mineral group, in which Mg is on an inversion centre and the Ca, P and F/OH atoms are on twofold axes. The structure is composed of kinked chains of corner-sharing MgO(4)F(2) octahedra that are crosslinked by isolated PO(4) tetrahedra, forming a three-dimensional polyhedral network. The Ca(2+) cations occupy the interstitial sites coordinated by six O atoms and one F anion.
authors.affiliation: Department of Geosciences, University of Arizona, 1040 East 4th Street, Tucson, AZ 85721-0077, USA. hyang@u.arizona.edu
authors.forename: Hexiong
authors.initials: H
authors.lastname: Yang
authors.forename: Justin
authors.initials: J
authors.lastname: Zwick
authors.forename: Robert T
authors.initials: RT
authors.lastname: Downs
authors.forename: Gelu
authors.initials: G
authors.lastname: Costin