Rietveld structure refinement of synthetic strontium-rich potassium-richterites
Robert, Jean-Louis; Della Ventura, Giancarlο; Raudsepp, Mati; Hawthorne, Frank C.
European Journal of Mineralogy Volume 5 Number 2 (1993), p. 199 - 206
published: Apr 27, 1993
manuscript accepted: Nov 20, 1992
manuscript received: Feb 3, 1992
ArtNo. ESP147050502002, Price: 29.00 €
Abstract Complete substitution of Ca by Sr has been experimentally obtained at 750°C, 1 kbar in hydroxyl potassium-richterite. The refinement of the site occupancies by the whole-powder-pattern refinement method (Rietveld method) shows Sr to be completely ordered at the M(4) site. Cell parameters vary as a function of the Sr -> Ca substitution in a strongly anisotropic way: a and b increase whereas c remains constant. There is also a major increase in the ß angle. The variation of distance is linear. The structure refinements are good in the space group C2/m with the usual amphibole unit cell; in addition, there is no evidence for the existence of a supercell. Thus Ca and Sr show no evidence of any long-range ordering