Refinement of Mn-Substituted Muscovite and Phlogopite

Rick A. Knurr and S. W. Bailey
Department of Geology and Geophysics, University of Wisconsin-Madison Madison, Wisconsin 53706

Abstract: The crystal structures of a reddish-purple, Mn-bearing muscovite-2M1 (alurgite variety) and a reddish-brown, Mn-bearing phlogopite-1M (manganophyllite variety) were refined to final residuals of 2.7% and 3.1%, respectively. The refinements were carried out in space groups C2/c and C1 for alurgite and C2/m and C2 for manganophyllite. The C1 and C2 subgroup refinements gave atomic coordinates consistent with the parent space group refinements. No cation ordering was found in either specimen, and the structures are very similar to those of muscovite and phlogopite. Residual areas of positive electron densities were found between the tetrahedral cations and neighboring oxygens in difference maps of both minerals. Those of alurgite were examined in detail to show the correlation between the residual densities and covalent bonding in the tetrahedra. The valence of the Fe present was determined by Mössbauer spectra as Fe3+ in both samples and of the Mn by optical spectra as Mn3+ in the alurgite but as Mn2+ in the manganophyllite.

Key Words: Alurgite • Crystal structure • Manganese • Manganophyllite • Muscovite • Phlogopite

Clays and Clay Minerals; February 1986 v. 34; no. 1; p. 7-16; DOI: 10.1346/CCMN.1986.0340102
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)