Monazite-(Sm), a new member of the monazite group from the Annie Claim #3 granitic pegmatite, southeastern Manitoba

Monazite-(Sm) was found in the Annie Claim #3 pod of lepidolite-subtype granitic pegmatite within the Greer Lake intrusion of pegmatitic leucogranite, in the Archean Bird River Subprovince of the Superior Province, in southeastern Manitoba. It occurs as tabular crystals less than or equal to0.4 mm in diameter, associated with manganocolumbite, quartz, albite and lithian muscovite. Monazite-(Sm) is yellowish, translucent, with a white streak, vitreous to greasy luster, and no observed fluorescence. One good cleavage is present, tenacity is brittle, and the fracture is uneven. Monazite-(Sm) has no observable pleochroism; alpha 1.768 (5), beta 1.771(3), gamma > 1.808(3); 2V(meas) 29(8)degrees, X = b, Z Lambda c = 9degrees (beta obtuse). It is monoclinic, space group P2(1)/n; a refinement from single-crystal and powder (Gandolfi) X-ray-diffraction data gave a 6.725(1), 6.739(3), b 6.936(1), 6.951(3), c 6.448(1), 6462(3) Angstrom, beta 104.02(1)degrees, 104.03(4)degrees, V 291.8(1), 293.6(2) Angstrom(3), Z = 4; D-calc derived from average chemical composition is 5.512 and 5.478 g/cm(3). The strongest six lines of the (Gandolfi) X-ray-diffraction pattern [d in Angstrom(l)(hkl)] are: 4.647(5)(011),4.164(8)((1) over bar 11), 3.492(4)(111,020), 3.264(7)(200), 3.065(10)(120), and 2.857(9)((1) over bar 12 ,012). The monazite-(Sm) contains, in wt.%, up to 14.29 Sm2O3, 13.48 Gd2O3 and 6.28 Nd2O3, and moderate percentages of the huttonite and brabantite components. The most Sm-rich composition gives (Sm0.197Gd0.179Ce0.148Th0.125Ca0.107Nd0.090La0.030Y0.030Pr0.023Tb0.017Zr0.017Dy0.016Pb0.016U0.002)(Sigma0.997) (P-0.963 Si-0.044)(Sigma1.007) O-4. Adjustment of U and Th of the monazite-(Sm) to their original contents 2.64 Ga ago slightly improves the stoichiometry and proves that all the Ph present is radiogenic. The middle-REE-dominant signature of the Annie Claim #3 monazite-(Sm) is shared with the broadly associated Y(Ta,Nb)O-4 mineral (formanite?) and dysprosian xenotime-(Y); this exotic pattern of REE abundances is possibly generated by selective and differential complexing of REE in the granite-to-pegmatite sequence of solidification.