The new mineral species suseinargiuite, (Na0.5Bi0.5)MoO4, has been discovered in the Mo-Bi occurrence of Su Seinargiu, Sarroch, Cagliari, Sardinia, Italy. It occurs as hemispherical aggregates of very small acicular crystals, up to some micrometres in length. It is colourless, with a pearly to adamantine lustre. In the studied specimens, suseinargiuite is associated with wulfenite. Micro-Raman spectra were collected in the region between 100 and 2000 cm−1. The following bands have been observed (in cm−1): 131, 188, 319, ~ 376, ~ 772, and 876. Electron microprobe data collected on a chemically zoned grain gave (outer and inner zone, respectively – in wt%): MoO3 49.03, Bi2O3 42.97, PbO 2.89, Na2O 3.69, total 98.58, and MoO3 45.59, Bi2O3 34.47, PbO 12.04, Na2O 3.03, total 95.13. On the basis of 4 O atoms per formula unit, the chemical formulae are (Na0.35Bi0.54Pb0.04) Σ=0.93Mo0.99O4 and (Na0.31Bi0.46Pb0.17) Σ=0.94Mo0.99O4, respectively. Main diffraction lines are [d in Å (relative intensity) hkl]: 3.146 (100) 112, 2.912 (13) 004, 2.652 (18) 200, 1.964 (34) 204, 1.875 (15) 220, 1.728 (19) 116, and 1.616 (28) 312 and 132. Unit-cell parameters, refined from the powder X-ray diffraction data in a tetragonal setting, space group I41/a, are a = 5.296(1), c = 11.673(2) Å, V = 327.4(1) Å3, Z = 4. Owing to the lack of suitable crystals and the very small amount of available material, the crystal structure of suseinargiuite was not solved. However, X-ray powder diffraction data, micro-Raman spectra, as well as chemical analysis, show the close correspondence between suseinargiuite with synthetic (Na0.5Bi0.5)MoO4, which displays a scheelite-type structure.

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