Synthesis, XRD and FTIR studies of strontium richterites
Della Ventura, Giancarlo; Robert, Jean-Louis
European Journal of Mineralogy Volume 2 Number 2 (1990), p. 171 - 176
published: Apr 17, 1990
manuscript accepted: Nov 28, 1989
manuscript received: Jul 27, 1989
ArtNo. ESP147050202003, Price: 29.00 €
Abstract An infrared investigation of hydrothermally prepared Sr-substituted Na and K richterites is presented. X-ray powder data show a notable increase of the a, b, and β parameters due to the larger ionic radius of eight-fold coordinated Sr2+ with respect to Ca2+. The infrared spectra rule out the presence of Sr2+ in the A-site, thus demonstrating that strontium should be allotted to the M(4) site. In the spectrum of Na-Sr-richterite, the major-intensity band is split into two components, at 3730 and 3725 cm-1 , and a tremolite-type band is observed at 3670 cm-1 due to OH dipoles pointing towards apparently vacant A-sites. The potassic strontium end-member exhibits a single sharp band at 3735 cm-1 in the region of OH-stretching wavenumbers. These observations are discussed in terms of local polyhedral geometry. The usefulness of infrared spectroscopy is stressed for defining local structural features, at least in chemically simple amphiboles.