Crystal Structure Modeling of a Highly Disordered Potassium Birnessite

Kerry L. Holland and Jeffrey R. Walker
Department of Geology and Geography, Vassar College, Poughkeepsie, New York 12601
Present address: Colorado School of Mines, Boulder, Colorado.

Abstract: The structure of a highly disordered synthetic birnessite was studied by comparing powder X-ray diffraction (XRD) data with calculated patterns generated by BIRNDIF and WILDFIRE© in an attempt to describe the nature of disorder and to estimate the size of the coherent diffracting domains. The material has a turbostratic stacking sequence and coherent diffracting domains that are 25 to 30 Å on a side in the ab plane (N1 = 5 unit cells, N2 = 10 unit cells) and which average 2.5 unit cells thick parallel to c. Turbostratic stacking probably results because there are few constraints on the relationship between adjacent layers.

Key Words: Birnessite • Crystal Structure Modeling • Turbostratic Stacking

Clays and Clay Minerals; December 1996 v. 44; no. 6; p. 744-748; DOI: 10.1346/CCMN.1996.0440604
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)