The crystal structure of tokkoite and its relation to the structure of tinaksite

• Published in: Zeitschrift für Kristallographie - Crystalline Materials
• Other Authors: Rozhdestvenskaya, I. V., Nikishova, L. V., Lazebnik, Yu. D., Lazebnik, K. A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Walter de Gruyter GmbH 1989
• Subjects: Inorganic Chemistry; Condensed Matter Physics; General Materials Science; Yakutia
• Online Access: http://dx.doi.org/10.1524/zkri.1989.189.3-4.195; https://www.degruyter.com/document/doi/10.1524/zkri.1989.189.3-4.195/xml; https://www.degruyter.com/document/doi/10.1524/zkri.1989.189.3-4.195/pdf

Abstract Tokkoite, K 2 Ca 4 [Si 7 O 18 (OH)](F,OH), a new mineral from Murun massif, South Yakutia, USSR, is triclinic with unit-cell dimensions a = 1.0438(3) nm, b = 1.2511(3) nm, c = 0.7112(2) nm, α = 89.92(2)°, β = 99.75(2)°, γ = 92.89(2)°, space group P [unk], Z = 2. The crystal structure has been determined by the Patterson method and difference Fourier maps followed by a least-squares refinement to an R factor of 0.032 for 906 ( I > 1.96 σ I ) reflections measured on an automatic single-crystal X-ray diffractometer. The structure consists of corrugated walls of calcium octahedra parallel to (100), between which bands of silicon – oxygen tetrahedra are situated. One of the non-bridging end anions is a OH group. K atoms are located within zig-zag channels formed by curved silicate bands. Tokkoite and tinaksite, K 2 Ca 2 NaTi [Si 7 O 18 (OH)]O, are isostructural. These two structures are related by the substitution 2Ca 2+ ⇌Ti 4+ + Na + and (F,OH) − ⇌ O 2− which occurs simultaneously in kationic and anionic parts of minerals. Common structural details of tokkoite, miserite and canasite are also considered.