We describe here the synthesis of amphiboles along the nominal Na(NaMg)Mg5Si8O22(OH)(2)- Na(LiMg)Mg5Si8O22(OH)(2) join, at 800 degrees C, 0.4 GPa. High amphibole yields (> 90%) plus minor quartz and enstatite have been obtained at all compositions; amphibole crystals are acicular and their size rarely exceeds 20-30 X 0.5-3 mu m. TEM analysis shows the presence of h+k odd reflections in all samples, indicative of a P-lattice. By similarity with closely related amphiboles from the literature (c,g., Oberti et al. 2000; Camara et al. 2003) it P2(1)/m space group was assigned to the amphiboles synthesized here. Refined cell-parameters from X-ray powder-patterns show a linear decrease as a function of increasing Li at M4, a and P being the most affected parameters. The four infrared OH-stretching spectra all show two main bands at 3741-3748 and 3712-3716 cm(-1), respectively. They are assigned to two independent O-H groups in the P2(1)/m structure, interacting with a strongly delocalized Na-A. The spectra show in addition two minor absorptions at about 3688 and 3667 cm(-1), respectively; these bands are assigned to vacant A-sites in the structure and indicate slight departure of the nominal composition toward cummingtonite. The present work shows that one apfu of Na-B can also be completely replaced by one apfu of Li-B (M+), in synthetic Na(M+Mg)Mg5Si8O22(OH)(2) and that all compositions have P2(1)/m symmetry at ambient conditions.
Iezzi, G., DELLA VENTURA, G., Tribaudino, M. (2006). Synthetic P21/m amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O (LNMSH). AMERICAN MINERALOGIST, 91, 425-429 [10.2138/am.2006.1964].
Synthetic P21/m amphiboles in the system Li2O-Na2O-MgO-SiO2-H2O (LNMSH)
DELLA VENTURA, Giancarlo;
2006-01-01
Abstract
We describe here the synthesis of amphiboles along the nominal Na(NaMg)Mg5Si8O22(OH)(2)- Na(LiMg)Mg5Si8O22(OH)(2) join, at 800 degrees C, 0.4 GPa. High amphibole yields (> 90%) plus minor quartz and enstatite have been obtained at all compositions; amphibole crystals are acicular and their size rarely exceeds 20-30 X 0.5-3 mu m. TEM analysis shows the presence of h+k odd reflections in all samples, indicative of a P-lattice. By similarity with closely related amphiboles from the literature (c,g., Oberti et al. 2000; Camara et al. 2003) it P2(1)/m space group was assigned to the amphiboles synthesized here. Refined cell-parameters from X-ray powder-patterns show a linear decrease as a function of increasing Li at M4, a and P being the most affected parameters. The four infrared OH-stretching spectra all show two main bands at 3741-3748 and 3712-3716 cm(-1), respectively. They are assigned to two independent O-H groups in the P2(1)/m structure, interacting with a strongly delocalized Na-A. The spectra show in addition two minor absorptions at about 3688 and 3667 cm(-1), respectively; these bands are assigned to vacant A-sites in the structure and indicate slight departure of the nominal composition toward cummingtonite. The present work shows that one apfu of Na-B can also be completely replaced by one apfu of Li-B (M+), in synthetic Na(M+Mg)Mg5Si8O22(OH)(2) and that all compositions have P2(1)/m symmetry at ambient conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
