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Mineralogical ClassificationIMA 2004-001 = Samarskite-(Yb)
13th Nov 2006 11:51 UTCMarco E. Ciriotti Manager
• Simmons, W.B., Hanson, S.L., Falster, A.U. (2006): Samarskite-(Yb): a new species of the samarskite group from the Little Patsy pegmatite, Jefferson County, Colorado. Canadian Mineralogist, 44, 1119-1125.
Abstract:
Samarskite-(Yb) occurs at the Little Patsy NYF-type granitic pegmatite in the South Platte district, Jefferson County, Colorado as black, metamict, anhedral masses up to tens of centimeters across that are intimately intergrown with ferrocolumbite and zircon. It occurs in late-stage replacement units at the core–margin contact within the pegmatite, and is associated with ishikawaite, samarskite-(Y), zircon, columbite, monazite-(Ce) and yttrian fluorite. Samarskite-(Yb) is black with a brown to black streak, and isotropic with an index of refraction greater than 2.1. It is brittle with a hardness of between 5 and 6. It exhibits a vitreous luster, is nearly opaque, and non-fluorescent in ultraviolet light. It has no cleavage, and exhibits a conchoidal fracture. Twinning was not observed. Upon heating to 1100°C for 12 hours, the mineral recrystallizes to a monoclinic form with unit-cell parameters like those of other samarskite-group minerals recrystallized under the same weakly reducing conditions at the same temperature: a 5.688(9), b 9.915(2), c 5.199(9) Å, b 93.16(10)°, and V 292.760 Å3. The strongest six lines in the X-ray powder-diffraction pattern are: 2.971(100)(121), 3.070(25)(21), 3.664(21)(¯111), 1.870(20)(202), 1.574(20)(160), and 1.769(15)(320). The measured density of an unheated sample is 7.03(1) g/cm3. The density calculated from the empirical formula with Z = 4 is 7.079 g/cm3. Electron-microprobe analyses gave (in wt.%): Nb2O5 29.53, Ta2O5 15.13, TiO2 0.64, ThO2 10.11, UO2 10.39, La2O3 0.03, Ce2O3 0.22, Pr2O3 0.05, Nd2O3 0.64, Sm2O3 0.42, Gd2O3 0.55, Tb2O3 0.25, Dy2O3 3.16, Ho2O3 0.59, Er2O3 3.40, Tm2O3 0.58, Yb2O3 5.78, Lu2O3 0.97, Y2O3 1.92, MnO 1.02, ZrO2 0.98, CaO 2.11, Sc2O3 0.26, SnO2 0.54, PbO 0.27, WO3 2.96, FeO 2.55, SiO2 0.41, sum = 95.37 wt%, which corresponds to the empirical formula: (S0.341 U0.126 Th0.125 Ca0.123 Fe2+0.116 Mn0.047 W0.042 Zr0.026 Si0.022 Sc0.012 Sn0.012 Pb0.004)S0.996 (Nb0.728 Ta0.224 Ti0.027)S0.979 O4. The simplified formula is (Yb,Y,REE,U,Th,Ca,Fe2+) (Nb,Ta,Ti) O4, and the ideal formula is YbNbO4. Samarskite-(Yb) was approved by the IMA Commission on New Minerals and Mineral Names (2004–001).
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