Wakefieldite-(La), LaVO (sub 4) , a new mineral species from the Gluecksstern Mine, Friedrichroda, Thuringia, Germany

Wakefieldite-(La), ideally LaVO (sub 4) , is a new mineral from the long abandoned Glucksstern Mine, Gottlob hill, Friedrichroda, Thuringia, Germany. The mineral occurs as light pinkish to brown prismatic crystals up to 0.5 mm in length. Wakefieldite-(La) is associated with hausmannite, baryte and gottlobite. The streak is white, the Mohs hardness 4 and the luster adamantine. The crystals are transparent to translucent. Electron microprobe analysis gave (wt.%) La (sub 2) O (sub 3) 43.87, Ce (sub 2) O (sub 3) 0.31, Nd (sub 2) O (sub 3) 9.49, Pr (sub 2) O (sub 3) 6.65, Sm (sub 2) O (sub 3) 0.58, Y (sub 2) O (sub 3) 0.31, CaO 0.10, UO (sub 2) 0.01, V (sub 2) O (sub 5) 34.91, As (sub 2) O (sub 5) 0.06, P (sub 2) O (sub 5) 0.02, SiO (sub 2) 0.04, total 96.35. The empirical formula is (La (sub 0.71) Nd (sub 0.15) Pr (sub 0.11) Sm (sub 0.01) Y (sub 0.01) ) (sub Sigma 0.99) V (sub 1.01) O (sub 4.00) , ideally LaVO (sub 4) . The new mineral (IMA 89-035a) is the La analogue of wakefieldite-(Ce) and wakefieldite-(Y) and a member of the xenotime group. Wakefieldite-(La) has a zircon-type crystal structure (tetragonal, space group,I4 (sub 1) /amd), with a = 7.406(4), c = 6.504(8) Aa, V = 356.8(6) Aa (super 3) from X-ray powder diffraction data and a = 7.432(1), c = 6.521(1) Aa, V = 360.18(9) Aa (super 3) from the single-crystal structure refinement (R (sub 1) = 1.04 %). The La site is eight-coordinated to O atoms, with La-O distances of 2.4558(13) Aa (x 4) and 2.5381(14) Aa (x 4). The V-O distance equals 1.7133(13) Aa (x 4). The calculated density for the measured composition is 4.703 g/cm (super 3) . Wakefieldite-(La) is uniaxial positive with omega and epsilon >1.90, birefringence is medium, pleochroism E pale pinkish and O pale pinkish yellow.