Parisite-(Nd), ideally CaNd₂(CO₃)₃F₂, a new mineral from Bayan Obo FeNbREE deposit, Inner Mongolia, China

Abstract Parisite-(Nd) (IMA2024-013), ideally CaNd 2 (CO 3 ) 3 F 2 , as the Nd-dominant analogue of parisite-(Ce), occurs in dolomitic marble in the Bayan Obo Fe–Nb–REE deposit, Inner Mongolia, China. It is associated with calcite, aegirine, magnetite, hematite, fluorite, riebeckite, bastnäsite-(Ce), baryte, aeschynite-(Ce), aeschynite-(Nd), monazite and parisite-(Ce). Parisite-(Nd) occurs as subhedral to anhedral irregular grains from 0.02 mm to 1 mm. Parisite-(Nd) is transparent, yellowish-brown colour, with pale yellow streak and displays vitreous to resinous lustre. Cleavage is distinct on pseudo-{001}; fracture is uneven, or conchoidal. The Mohs hardness is 4 to 5, and it is brittle. The calculated density of parisite-(Nd) is 4.357 g/cm 3 . Parisite-(Nd) is pseudo-uniaxial (+), ω = (1.679) and ε = (1.754). The empirical formula is (Ca 0.945 Fe 0.058 Sr 0.015 Ba 0.007 ) Σ1.025 (Nd 0.967 Ce 0.529 La 0.191 Pr 0.137 Gd 0.070 Sm 0.029 Th 0.022 Y 0.016 Nb 0.011 Ho 0.003 ) Σ1.975 (CO 3 ) 3 F 1.893 OH 0.023. The Raman spectra of parisite-(Nd) show strong and sharp peaks at 1113, 1090, 825, 635 and 1608 cm –1 and moderate to weak bands centred at 255, 392, 739, 924, 1183, 1228, 1296, 1640, 2247, 2924 and 3065 cm –1 . Powder X-ray diffraction and TEM studies give the following results: monoclinic, space group: Cc (# 9), a = 12.3283(13) Å, b = 7.1185(4) Å, c = 28.4633(37) Å, β = 98.529(14)°, V = 2470.28(42) Å 3 and Z = 12.