CRYSTAL-STRUCTURE REFINEMENT OF BOROMUSCOVITE POLYTYPES USING A
COUPLED RIETVELD - STATIC-STRUCTURE ENERGY-MINIMIZATION METHOD
JIAN-JIE LIANG, FRANK C. HAWTHORNE, MILAN NOVÁK* and PETR CERNÝ
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2
LUISA OTTOLINI
CNR Centro di Studio per la Cristallochimica e la Cristallografia,
Via Abbiategrasso 209, 27100 Pavia, Italy
* Permanent address: Department of Mineralogy and Petrology, Moravian Museum, Zelný trh 6, 659 37 Brno,
Czech Republic.
Abstract
Boromuscovite from the Little Three mine granitic pegmatite, California, occurs only as
very fine- grained aggregates, and is a mixture of 2M1 and 1M polytypes. Crystal structures of both
polytypes have been simultaneously refined in space groups C2/c and C2/m, respectively, using
a coupled Rietveld - static-structure energy-minimization method. Intensity data were collected on a
high-resolution powder diffractometer in transmission geometry, with the sample prepared such
that preferred orientation is largely avoided. The refinement converged to Rwp = 13.8% (Rexp = 7.9%),
RBRG (2M1) = 3.8%, and RBRG (1M) = 3.8%. Boron is evenly distributed between the two polytypes,
and distances correspond well with the B-content at the corresponding T-sites.
Keywords: boromuscovite, Rietveld structure refinement, chemical analysis, polytype, energy minimization.