The aim of this project is to study the atomic surface structure of a natural muscovite crystal thanks to the synchrotron radiation light and the grazing incidence X-ray diffraction (GIXRD).The muscovite studied [(K0.92Na0.08) (Al1.86Fe3+0.01Mg.0.07 Fe2+0.06Ti0.02) (Si3.03Al0.97) O10 F0.09 (OH)1.91] is monoclinic, 2M1 polytype, with symmetry C2/c and unit cell parameters a = 5.19690(10) b = 9.0138(3) c = 20.0835(7) (Å) and β = 95.763(2) (°).The muscovite structure was refined by single crystal X-ray diffraction and the final refinement yielded the following agreement factor R = 0.0299. The difference Fourier map shows a significant residual electron density (2.2-) close to the position related to M1 site, thus indicating that the excess of octahedral cations is located at M1. M1-O mean bond distance is 2.247(9) and M2-O distance is 1.929.Grazing incidence X-ray diffraction (GIXRD) was recently performed at SpLine at ESRF. This type of analysis is very useful to identify typical structural features of the surface, such as possible imperfections, relaxations or reconstructions. Usually, the atoms on surfaces, and sometimes those as deep as several layers down, assume positions different from their equilibrium positions in the bulk. Generally mineral surfaces will not be reconstructed unless they have been heated to temperature higher than 100 °C. In our case, the muscovite surface has been exposed to a delay of the first layer in order to study a freshly cleaned surface and data collected by GIXRD confirm that on muscovite surface only a relaxation occurs from an equivalent plane in the bulk. This is a common case for minerals with a low-symmetry structure as the feldspar surface.
Surface structure of natural muscovite / Elmi, Chiara; Brigatti, Maria Franca; Malferrari, Daniele; Castro, G. R.; Ferrer Escorihuela, P.. - ELETTRONICO. - 6:(2010), pp. 753-753. (Intervento presentato al convegno IMA 2010, 20th General Meeting of the International Mineralogical Association tenutosi a Budapest (Ungheria) nel 21-27 Agosto 2010).