We present the crystal chemical characterization of fluorannite from Katugin Ta-Nb deposit, Chitinskaya Oblast’, Kalar Range, Transbaikalia, Eastern-Siberian Region, Russia. This mica belongs to 1M polytype (space group C2/m) with layer parameters a = 5.3454(2) Å, b = 9.2607(4) Å, c = 10.2040(5) Å, ? = 100.169(3)°. Structure refinement, using anisotropic displacement parameters, converged at R = 0.0384. Fluorannite shows a smaller cell volume (V = 497.19 Å3) than annite (V = 505.71 Å3) because of its smaller lateral dimensions and its reduced c parameter. The flattening of the tetrahedral basal oxygen atoms plane decreases with F content, together with the A-O4 distance (i.e., the distance between interlayer A cation and the octahedral anionic position) because of the reduced repulsion between the interlayer cation and the anion sited in O4.
Brigatti, M.F., Caprilli, E., Malferrari, D., Mottana, A. (2007). Crystal structure and crystal chemistry of fluorannite and its relationships to annite. MINERALOGICAL MAGAZINE, 71, 732-745.
Crystal structure and crystal chemistry of fluorannite and its relationships to annite
MOTTANA, Annibale
2007-01-01
Abstract
We present the crystal chemical characterization of fluorannite from Katugin Ta-Nb deposit, Chitinskaya Oblast’, Kalar Range, Transbaikalia, Eastern-Siberian Region, Russia. This mica belongs to 1M polytype (space group C2/m) with layer parameters a = 5.3454(2) Å, b = 9.2607(4) Å, c = 10.2040(5) Å, ? = 100.169(3)°. Structure refinement, using anisotropic displacement parameters, converged at R = 0.0384. Fluorannite shows a smaller cell volume (V = 497.19 Å3) than annite (V = 505.71 Å3) because of its smaller lateral dimensions and its reduced c parameter. The flattening of the tetrahedral basal oxygen atoms plane decreases with F content, together with the A-O4 distance (i.e., the distance between interlayer A cation and the octahedral anionic position) because of the reduced repulsion between the interlayer cation and the anion sited in O4.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
