Bastnasite-(Nd), a new Nd-dominant member of the bastnasite group from the Stetind Pegmatite, Tysfjord, Nordland, Norway

Bastnasite-(Nd), ideally (Nd,La,Ce)(CO (sub 3) )F, occurs in the Stetind pegmatite, Tysfjord, Nordland, Norway, in association with bastnasite-(Ce), calcioancylite-(Nd) and/or kozoite-(Nd), stetindite, vyuntspakhkite-(Y) and Y-bearing fluorite. It forms 20 mu m wide zones in outer parts of tabular bastnasite-(Ce) crystals. Bastnasite-(Nd) is translucent and is pale purplish pink to colourless with a vitreous, greasy or pearly lustre. Bastnasite-(Nd) has a Mohs hardness of 4-4 1/2, is brittle, and shows an indistinct cleavage on {1010} and an uneven fracture. The calculated density and mean refractive index are 5.23 g cm (super -3) and 1.76, respectively. It is hexagonal, space group P62c, a = 7.0792(13), c = 9.721(2) Aa, V = 421.92(18) Aa (super 3) and Z = 6. The five strongest lines in the powder XRD pattern are [d(Aa), I/I (sub 0) , hkl]: 4.86, 71, 002; 3.54, 70, 110; 2.86, 100, 112; 2.04, 31, 300 and 2.00, 48, 114. The electron-microprobe analyses lead to the empirical formula (on the basis of M = C = 1 apfu): Nd (sub 0.353) La (sub 0.253) Ce (sub 0.251) Pr (sub 0.086) Sm (sub 0.037) Gd (sub 0.016) Y (sub 0.004) Dy (sub 0.001) CO (sub 2.978) F (sub 1.044) . Bastnasite-(Nd) is a member of the bastnasite group, and is the Nd-dominant analogue of bastnasite-(Ce), bastnasite-(La) and bastnasite-(Y). Bastnasite-(Nd) formed as a late phase in cavities in Y-bearing fluorite, which in turn is a late formation of the pegmatite.