Abstract: Hydroxyl-bastnaesite-(Nd), the Nd- and OH-dominant new member of the bastnaesite group, has been found in the red karstic bauxites near Nikšić, Montenegro. It occurs as whitish, irregular aggregates of crystals usually 100–200 µm in diameter. Hexagonal with the cell dimensions a = 7.191 and c = 9.921 Å, with Z = 6. The strongest lines of the X-ray powder diffraction pattern (d, I, hkl) are: 4.95 80(002); 3.596 79(110); 2.911 100(112); 2.077 29(300); 2.042 51(114); 1.914 30(302). The mineral is uniaxial positive, ω 1.715, ɛ 1.81; D_calc 4.89 g/cm³.

Electron probe analysis, using garnet, apatite and synthetic glass standards, combined with thermogravimetric and evolved gas analysis, gave Y₂O₃ 0.2, La₂O₃ 27.1, Ce₂O₃ 0.3, Pr₂O₃ 8.5, Nd₂O₃ 31.5, Sm₂O₃ 4.4, Eu₂O₃ 1.3, Gd₂O₃ 1.4, CaO 0.3, F 3.3, H₂O 2.26, CO₂ 20.63, sum 101.19, less O = F 1.39, total 99.80%. This analysis calculates to (Nd_0.41La_0.36Pr_0.11Sm_0.06Gd_0.02 Eu_0.02Ca_0.01)_Σ0.99(CO₃)_1.03[(OH)_0.55F_0.38]_Σ0.93, or ideally, (Nd,La)CO₃(OH,F), with Nd > La and OH > F.