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Published online by Cambridge University Press: 31 January 2025
Two alluaudite-group minerals, badalovite, ideally NaNaMg(MgFe3+)(AsO4)3, and calciojohillerite, NaCaMgMg2(AsO4)3, have been identified on a specimen from the Monte Calvario quarry, Biancavilla, Etna volcanic complex, Sicily, Italy. For both species, this finding represents the second world occurrence. The studied sample was characterised using electron microprobe analysis, micro-Raman spectroscopy, and single-crystal X-ray diffraction. Badalovite occurs as vitreous to resinous aggregates of yellowish to brownish prismatic crystals, up to 0.5 mm in length, associated with tabular crystals of hematite, pseudobrookite and an amphibole-supergroup mineral. Badalovite is intimately intergrown with minor calciojohillerite. The chemical formulae of these two alluaudite-group members, recalculated on the basis of 12 O atoms per formula unit and assuming the occurrence of Fe3+, are (Na1.74(11)K0.01(1)Ca0.30(8))Ʃ2.05(Mg1.74(2)Mn0.27(2)Ca0.11(8)Zn0.03(1)Fe0.84(14)Al0.02(2))Ʃ3.01(As2.85(4)P0.11(3))Ʃ2.96O12 and (Na1.44(2)K0.01(1)Ca0.66(1))Ʃ2.11(Mg2.27(1)Mn0.28(1)Zn0.01(1)Fe0.48(2))Ʃ3.00(As2.79(3)P0.13(2))Ʃ2.92O12, respectively. Single-crystal X-ray diffraction data collected on badalovite gave the following unit-cell parameters a = 11.9760(5), b = 12.7857(5), c = 6.6650(3) Å, β = 112.689(2)°, V = 941.58(7) Å3, space group C2/c. Its crystal structure was refined to R1 = 0.0257 for 1711 unique reflections with Fo > 4σ(Fo) and 97 least-square parameters. The crystal chemical and spectroscopic data as well as the genesis of badalovite are discussed and a comparison with the Russian type material is reported.
Associate Editor: Peter Leverett