Site occupancies in synthetic monoclinic amphiboles; Rietveld structure refinement and infrared spectroscopy of (nickel, magnesium, cobalt)-richterite

Abstract

Other| April 01, 1997 Site occupancies in synthetic monoclinic amphiboles; Rietveld structure refinement and infrared spectroscopy of (nickel, magnesium, cobalt)-richterite Giancarlo Della Ventura; Giancarlo Della Ventura Terza Universita di Roma, Dipartimento di Scienze Geologiche, Rome, Italy Search for other works by this author on: GSW Google Scholar Jean-Louis Robert; Jean-Louis Robert CNRS, France Search for other works by this author on: GSW Google Scholar Mati Raudsepp; Mati Raudsepp University of British Columbia, Canada Search for other works by this author on: GSW Google Scholar Frank C. Hawthorne; Frank C. Hawthorne University of Manitoba, Canada Search for other works by this author on: GSW Google Scholar Mark D. Welch Mark D. Welch Natural History Museum, United Kingdom Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (3-4): 291–301. https://doi.org/10.2138/am-1997-3-407 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Giancarlo Della Ventura, Jean-Louis Robert, Mati Raudsepp, Frank C. Hawthorne, Mark D. Welch; Site occupancies in synthetic monoclinic amphiboles; Rietveld structure refinement and infrared spectroscopy of (nickel, magnesium, cobalt)-richterite. American Mineralogist 1997;; 82 (3-4): 291–301. doi: https://doi.org/10.2138/am-1997-3-407 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Amphiboles were synthesized at 750 °C, 1 kbar (H2O) on the binary joins (nickel, magnesium)-richterite and (magnesium, cobalt)-richterite. Structural variations and site occupancies were characterized by Rietveld structure refinement, with final RBragg indices in the range 4–9%, and by powder infrared spectroscopy in the principal OH-stretching region. Site-occupancy refinement of Ni-Mg and Mg-Co distributions give the partition coefficients over M1,3 and M2 where KM2+ = (M2+/Mg)M1,3/(M2+/Mg)M2, and M2+ = Ni2+ or Co2+, KdNi = 2.98 ± 0.37 and KdCo = 1.34 ± 0.31⁠. Both Kd values are greater than 1.0, whereas [6]r(Ni2+) < [6]r(Mg) < [6]r(Co2+); this indicates that cation size is not the primary factor affecting the ordering of Ni-Mg and Mg-Co over the octahedral sites. The infrared spectra of intermediate binary compositions show fine structure caused by ordering of Ni-Mg or Mg-Co over the M1,3 sites and by ordering of Na and □ (vacancy) at the A site; thus intermediate compositions show an eight-band spectrum in the principal OH-stretching region. Precise band intensities were derived by nonlinear least-squares fitting of Gaussian band shapes to the observed spectra. The relative observed intensities of the combinations of bands 3IoA+2IoB+IoC and IoB+2IoC+3IoD are in accord with the equations of Burns and Strens (1966), indicating that there is no significant variation in molar absorptivity with frequency (energy) for individual bands within a single sample (spectrum). Combined with the results of Skogby and Rossman (1991) on polarized single-crystal infrared spectra of amphiboles, this result suggests that different local configurations of M1,3 cations in amphiboles couple such that the transition probabilities of the associated OH groups are equal. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.