Grațianite, MnBi2S4, a new mineral from the Băița Bihor skarn, Romania.

The new mineral grațianite, MnBi2S4, is described from the Băița Bihor skarn deposit, Bihor County. Romania. Grațianite occurs as thin lamellae, intimately intergrown with cosalite and bismuthinite, or as flower-shaped blebs within chalcopyrite, where it is associated with cosalite and tetradymite. Grațianite displays weak to modest bireflectance in air and oil, respectively, and strong anisotropy. The mean empirical composition based on 20 electron probe microanalyses is: (Mn0.541Fe0.319Pb0.070Cu0.040 Cd0.009Ag0.001)Σ0.980(Bi1.975Sb0.018)Σ1.993(S4.008Se0.012Te0.007)Σ4.027, corresponding to the ideal formula MnBi2S4. Grațianite crystallizes in the monoclinic system (space group Cllm). Single-crystal X-ray studies of material extracted by the focused ion beam-scanning electron microscopy (FIB-SEM) technique, and carried out on the MX2 macromolecular beamline of the Australian Synchrotron determined the following cell dimensions: α = 12.6774(25) Å, b = 3.9140(8) Å, c = 14.7581(30) Å, β = 115.31(3)°, V= 662.0(2) ų, and Z = 4. The six strongest X-ray reflections and their relative intensities are: 3.448 Å (100), 2.731 Å (77), 2.855 Å (64), 3.637 Å (55), 3.644 Å (54), and 3.062 Å (51). Grațianite is the monoclinic analog of berthierite (FeSb2S4), garavellite [Fe(Bi,Sb)2S4] and clerite [Mn(SbAs)2S4] (Nickel-Strunz class 02.HA.20). It is isostructural with synthetic sulfides and selenides in the MnBi2S4-MnSb2S4 and MnBi2Se4-MnSb2Se4 series, and with grumiplucite (HgBi2S4) and ku-driavite, [(Cd,Pb)Bi2S4], ³P members of the pavonite homologous series. The mineral is named for Grațian Cioflica (1927-2002), formerly Professor in Mineralogy and Ore Deposits at the University of Bucharest, Romania. The Băița Bihor skarn, like others within the same belt, is geochemically complex. The availability of Cu, Zn, and Pb, but also Ag, Bi, Mo, and B, as well as a wide range of minor elements, has created an environment allowing for crystallization of an unusually diverse range of discrete minerals. Grațianite is part of the peculiar associations of Bi--Pb-sulfosalts and Bi-chalcogenides that are genetically related to Au-enrichment. This study demonstrates the versatility of FIB-SEM techniques for in situ extraction of small volumes of well-characterized material, coupled with single-crystal X-ray analysis using synchrotron radiation, for the characterization of new minerals. [ABSTRACT FROM AUTHOR]