HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Journal articles

First structure determination of an MDO-2O mica polytype associated with a 1M polytype

Abstract : The structure refinement of associated phlogopite-2O and phlogopite-1M from the Khibiny massif (Kola Peninsula, Russia) is reported. Crystal data are: a = 5.2781(5), b = 9.141(1), c = 20.124(4) Å, Ccmm (2O); a = 5.305(2), b = 9.199(2), c = 10.232(4) Å, β = 100.03(2)°, C2/m (1M). Least-squares refinement of single-crystal X-ray diffraction data converged to R1 = 0.034 (2O, 926 independent reflections) and 0.037 (1M, 677 independent reflections). This is the first structure refinement of an MDO (standard) mica-2O: two previous structure reports concerned anandite-2O, which was not a true polytype, having an oP (primitive orthorhombic) lattice not compatible with the C-centred cell common to all mica polytypes. The two phlogopite polytypes show practically the same chemical composition (K0.95Na0.01)(Mg2.16Fe0.34Ti0.04Mn0.04Li0.40)[Si3.40Al0.60O10][(OH)1.35F0.65] and no cation ordering. Both polytypes are affected by stacking disorder, which broadens the non-family reflections (k ≠ 3n). As a consequence, the diffracted intensities of the two types are measured at different scales and large residues in the difference Fourier maps were observed at ± b/3 along [010], [310] and [310]. These residues (Ďurovic effect) disappear by carrying out the refinement with separate scale factors for the two types of reflections. On the basis of structural, morphology and zoning considerations the formation of the two associated polytypes is attributed to chemical oscillation in the crystallization mean.
Complete list of metadata

Contributor : Massimo Nespolo Connect in order to contact the contributor
Submitted on : Wednesday, February 21, 2018 - 11:08:03 PM
Last modification on : Monday, February 7, 2022 - 4:06:04 PM




Giovanni Ferraris, Angela Gula, Gabriella Ivaldi, Massimo Nespolo, Elena Sokolova, et al.. First structure determination of an MDO-2O mica polytype associated with a 1M polytype. European Journal of Mineralogy, Copernicus, 2001, 13 (6), pp.1013 - 1023. ⟨10.1127/0935-1221/2001/0013-1013⟩. ⟨hal-01714834⟩



Record views