title: Disordered kalsilite KAlSiO4.
abstract: The X-ray powder diffraction pattern that corresponds to the disordered state of kalsilite (potassium aluminium orthosilicate), KAlSiO4, is investigated. The directionality of (Al,Si)O4 tetrahedra within single six-membered tetrahedral ring building units (S6R) could not be defined. With equal probability for the directionality of each tetrahedra within one S6R [free apex pointing up (U) or down (D)], an undefined sequence of U and D directionalities is needed to describe the S6R building units. The extinction conditions of disordered kalsilite are also different compared to ordered kalsilite within the space group P63. In disordered kalsilite, h0l and hhl reflections with l = 2n + 1 are systematically absent.
authors.affiliation: Laboratory of Crystallography, Faculty of Mining and Geology, University of Belgrade, Đušina 7, 11000 Belgrade, Serbia.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Kremenović
authors.affiliation: Laboratory of Crystallography, Faculty of Mining and Geology, University of Belgrade, Đušina 7, 11000 Belgrade, Serbia.
authors.forename: Predrag
authors.initials: P
authors.lastname: Vulić
keywords: crystal structure; disorder; kalsilite; potassium aluminium orthosilicate; powder diffraction; tetrahedra directionality