2026/04/14 by Irina Gałuskina, Irina O. Galuskina, Joachim Kusz +7
Earth and Planetary Sciences · Materials Science · #Crystal Structures and Properties #Mineralogy and Gemology Studies #Nuclear materials and radiation effects
paper · pdf · doi:10.1180/mgm.2026.10222
crossref issued 2026/04/14 · crossref published 2026/04/14 · crossref published-online 2026/04/14 · openalex publication_date 2026/04/14 · crossref created 2026/04/14 · openalex created_date 2026/04/15 · crossref published-print 2026/06/01 · openalex updated_date 2026/06/24 · crossref deposited 2026/07/17 · crossref indexed 2026/07/30
Abstract The new mineral, babunaite-(Nd) NdAsO 4 , was discovered in metasomatic rocks of the Mixed Series near the Nežilovo village in Northern Macedonia. These rocks are characterised by an unusual occurrence of Pb-Zn oxide ore mineralisation. This area forms part of the high-grade metamorphic region of the Upper Precambrian Pelagonian massif. Babunaite-(Nd) is an accessory mineral in pink schists, which mainly consists of Mn-bearing muscovite and quartz, with minor braunite. Accessory minerals are hematite, gahnite, almeidaite, långbanite, zircon, piemontite and piemontite-(Pb), nežilovite, Sb-bearing rutile, fluorapatite, As-bearing fluorapatite, gasparite-(La), chernovite-(Y), arsenoflorencite-(La). Babunaite-(Nd) forms single crystals measuring up to 70 μm in size. The transparent crystals exhibit an adamantine lustre and a pale-yellow colour. The microhardness of babunaite-(Nd) is VHN 25 = 578(21) kg/mm 2 , equivalent to a hardness of 5 on the Mohs scale. The mineral is brittle and does not exhibit cleavage. The mean composition of the holotype crystal is as follows: (Nd 3+ 0.39 Ca 0.14 Th 0.09 Pr 3+ 0.08 La 0.07 Sm 3+ 0.06 Y 0.06 Gd 0.05 Ce 3+ 0.02 Eu 3+ 0.01 ) Σ0.97 (As 5+ 0.95 W 6+ 0.05 V 5+ 0.01 ) Σ1.02 O 4 . The calculated density is 5.918 g·cm –3 . Babunaite-(Nd), with the general crystal chemical formula ABO 4 , has a scheelite-type structure and crystallises in the tetragonal I 4 1 / a space group: a = 5.1363(2) Å, c = 11.5764(8) Å, V = 305.41(3) Å 3 and Z = 4. The main bands at 190, 348, 440 and 833 cm –1 are distinguished in the Raman spectrum of babunaite-(Nd). A synthetic analogue of babunaite-(Nd) is known, which forms under high-pressure and high-temperature conditions of 11 GPa and 1100–1300°C. The genesis of the Mixed Series rocks occurred under metamorphic conditions approaching the parameters of the kyanite–graphite subfacies, at which gasparite-(Nd) with the monazite structure should form. The formation of babunaite-(Nd) is associated with the stabilisation of its structure by a tungsten (W) impurity. It is the first arsenate phase containing rare earth elements (REE) in the scheelite group.