%0 Journal Article %T Site occupancies in synthetic monoclinic amphiboles: Rietveld structure refinement and infrared spectroscopy of (nickel, magnesium, cobalt)-richterite. %+ Dipartimento di Scienze Geologiche [Roma TRE] %+ Institut des Sciences de la Terre d'Orléans (ISTO) %+ Department of Earth and Ocean Sciences [Vancouver] (EOS) %+ Department of Geological Sciences (DEPARTMENT OF GEOLOGICAL SCIENCES) %+ Department of Mineralogy %A Della Ventura, Giancarlo %A Robert, Jean-Louis %A Raudsepp, Mati %A C. Hawthorne, Franck %A Welch, Mark D. %< avec comité de lecture %@ 0003-004X %J The American Mineralogist %I Mineralogical Society of America %V 82 %P 291-301 %8 1997 %D 1997 %Z Sciences of the Universe [physics]/Earth Sciences/GeochemistryJournal articles %X Amphiboles were synthesized at 750 8C, 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 KM21 5 (M21/Mg)M1,3/(M21/Mg)M2, and M21 5 Ni21 or Co21, K 5 2.98 6 0.37 and K 5 1.34 6 0.31. Both Kd Ni Co values are greater than 1.0, d d whereas [6]r(Ni21 ) , [6]r(Mg) , [6]r(Co21 ); 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 M (vacancy) at the A site; thus intermediate compositions show an eight-band spectrum in the principal OHstretching 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 3IA1 2IB1 IC and IB 1 2IC 1 3ID are in accord with the equations o o o o o o 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. %G English %2 https://insu.hal.science/hal-00077576/document %2 https://insu.hal.science/hal-00077576/file/DellaVentura_p291-301_97.pdf %L hal-00077576 %U https://insu.hal.science/hal-00077576 %~ INSU %~ CNRS %~ UNIV-ORLEANS %~ ISTO %~ OSUC