Thermal strain analysis in the crystal structure of muscovite at 700 °C
Catti, Michele; Ferraris, Giovanni; Ivaldi, Gabriella
European Journal of Mineralogy Volume 1 Number 5 (1989), p. 625 - 632
published: Nov 16, 1989
manuscript accepted: Jun 9, 1989
manuscript received: Mar 7, 1989
ArtNo. ESP147050105002, Price: 29.00 €
Abstract The thermal dependence of the lattice constants of 2M1 muscovite, with the following formula: (K0.86 Na0.11)Σ0.97(Al1.93Fe0.07Mg0.02)Σ2.02(Al0.92Si3.08O10)(OH)2, was determined in the range 25-700°C by single-crystal X-ray diffractometry (MoKαradiation). 1.12, 1.18 and 1.89 × 10-5 K-1 were obtained as principal coefficients of thermal expansion. Intensity measurements were performed at 25 °C, yielding the cell parameters a = 5.191(1), b = 9.006(3), c =20.068(6) Å, ß = 95.77(2)° and at 700 °C yielding a = 5.229(1), b = 9.076(3), c =20.322(8) Å, ß = 95.74(3)° ; the crystal structure refinements, based on 1846 and 1046 observed reflections, gave R = 0.048 and 0.060, respectively. Results were analysed in terms of the lattice component and an inner component of the thermal structural strain. The inner strain is particularly large for basal oxygen atoms of the tetrahedral layer, consistent with the decrease of ditrigonal distortion, and within the coordination environment of K+ ions, with an overall tendency to higher symmetry for increasing temperature. The effects of the anisotropy of atomic thermal motion are also examined.