Lusernaite-(Y), Y,Al(CO,),(OH),,F~6H,0, is a new mineral from the Seccarezze quarries, Luserna Valley, Torino, Piedmont, Italy It occurs as colourless crystals and thin tablets, with mica-lilze pearly luster and roughly six-sided outline (Fig. 1). It is orthorhombic, space group Pmna, a = 7.8412(3), b = 11.0313(5), c = 11.3870(4) A. Crystals, elongated along [loo] and flattened on {OlO], are arranged in radiating aggregates. In the studied specimens, lusernaite- (Y) is associated with aeschynite-(Y), albite, "chlorite", hematite, pyrite, quartz, and titanite. The nature and the size of the available material did not allow the direct determination of H2O and CO2; however, the presence of the latter was confirmed through micro-Raman spectra. Unfortunately, due to strong luminescence, no detectable signals could be collected in the region of O-H vibrations. EPMA data point to the empirical formula (Y3.50Dy0.18Er0.14Yb0.09Gd0.07Sm0.01Pb0.01)Σ4.00Al1.00(CO3)2(OH)9.78F1.22∙6H2O, by assuming the presence of two (CO3)2- groups, eleven (OH,F)- anions, and six H2O molecules, in agreement with the structural results. The crystal structure of lusernaite-(Y) was solved through direct methods, using intensity data collected with an Oxford Gemini R Ultra diffractometer equipped with a CCD area detector. The refinement converged to R1 = 6.7% for 840 observed reflections and 89 parameters. The crystal structure may be described as formed by layers parallel to (010), composed by chains of edge-sharing Y1O8 polyhedra, running along [100], which are connected along c through AlO6 octahedra. Chains of Y1O8 polyhedra are decorated by edge-sharing with apex-sharing chains of Y2ϕ8 (ϕ = O,F,H2O) polyhedra on one side and by CO3 groups on the other. Polarity of chains - CO3 or Y2ϕ8 polyedra - alternates along [001] (Fig. 2). Lusernaite-(Y), named after the type locality (i.e. the Luserna Valley), shows a new kind of structure among the natural (fluoride)-carbonates of REE (Grice et al., 2007); it is also the first natural Y-A1 carbonate. Holotype material is kept in the mineralogical collections of the Mziseo di Storia Naturale e del Terriforio, University of Pisa, under catalogue number 19445. A cotype specimen is deposited in the Museo Regionale di Scienze Naturali, Turin, catalogue number 15901. References: Grice, J.D., Maisonneuve, V., Leblanc, M. (2007): Chem. Rev., 107, 114-132.
Lusernaite-(Y), Y4Al(CO3)2(OH)10F∙6H2O, a new mineral from Piedmont, Italy
CAMARA ARTIGAS, Fernando;
2012-01-01
Abstract
Lusernaite-(Y), Y,Al(CO,),(OH),,F~6H,0, is a new mineral from the Seccarezze quarries, Luserna Valley, Torino, Piedmont, Italy It occurs as colourless crystals and thin tablets, with mica-lilze pearly luster and roughly six-sided outline (Fig. 1). It is orthorhombic, space group Pmna, a = 7.8412(3), b = 11.0313(5), c = 11.3870(4) A. Crystals, elongated along [loo] and flattened on {OlO], are arranged in radiating aggregates. In the studied specimens, lusernaite- (Y) is associated with aeschynite-(Y), albite, "chlorite", hematite, pyrite, quartz, and titanite. The nature and the size of the available material did not allow the direct determination of H2O and CO2; however, the presence of the latter was confirmed through micro-Raman spectra. Unfortunately, due to strong luminescence, no detectable signals could be collected in the region of O-H vibrations. EPMA data point to the empirical formula (Y3.50Dy0.18Er0.14Yb0.09Gd0.07Sm0.01Pb0.01)Σ4.00Al1.00(CO3)2(OH)9.78F1.22∙6H2O, by assuming the presence of two (CO3)2- groups, eleven (OH,F)- anions, and six H2O molecules, in agreement with the structural results. The crystal structure of lusernaite-(Y) was solved through direct methods, using intensity data collected with an Oxford Gemini R Ultra diffractometer equipped with a CCD area detector. The refinement converged to R1 = 6.7% for 840 observed reflections and 89 parameters. The crystal structure may be described as formed by layers parallel to (010), composed by chains of edge-sharing Y1O8 polyhedra, running along [100], which are connected along c through AlO6 octahedra. Chains of Y1O8 polyhedra are decorated by edge-sharing with apex-sharing chains of Y2ϕ8 (ϕ = O,F,H2O) polyhedra on one side and by CO3 groups on the other. Polarity of chains - CO3 or Y2ϕ8 polyedra - alternates along [001] (Fig. 2). Lusernaite-(Y), named after the type locality (i.e. the Luserna Valley), shows a new kind of structure among the natural (fluoride)-carbonates of REE (Grice et al., 2007); it is also the first natural Y-A1 carbonate. Holotype material is kept in the mineralogical collections of the Mziseo di Storia Naturale e del Terriforio, University of Pisa, under catalogue number 19445. A cotype specimen is deposited in the Museo Regionale di Scienze Naturali, Turin, catalogue number 15901. References: Grice, J.D., Maisonneuve, V., Leblanc, M. (2007): Chem. Rev., 107, 114-132.
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