title: Monoclinic structure and nonstoichiometry of 'KAlSiO4-O1'.
abstract: Crystals of KAlSiO4-O1 (potassium aluminium silicate) were synthesized using a flux method and analysed utilizing single-crystal X-ray diffraction and electron microprobe analysis. Both methods confirm that the crystals are nonstoichiometric according to K(1-x)Al(1-x)Si(1+x)O4 with x = 0.04 (1). KAlSiO4-O1 is closely related to the stuffed derivatives of tridymite, although the topology of the Si/Al-ordered framework is different. Six-membered rings of UUDDUD and UUUDDD (U = up and D = down; ratio 2:1) configurations are present in layers parallel to the ab plane. In contrast, the framework of tridymite exhibits UDUDUD rings. The crystals are affected by inversion, pseudo-orthorhombic and pseudo-hexagonal twinning.
authors.affiliation: Laboratory of Crystallography, Faculty of Mining and Geology, University of Belgrade, Đušina 7, 11000 Belgrade, Serbia. akremen@EUnet.rs
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Kremenović
authors.forename: Biljana
authors.initials: B
authors.lastname: Lazic
authors.forename: Hannes
authors.initials: H
authors.lastname: Krüger
authors.forename: Martina
authors.initials: M
authors.lastname: Tribus
authors.forename: Predrag
authors.initials: P
authors.lastname: Vulić