The new mineral graţianite, MnBi2S4, is described from the Bǎi̧a Bihor skarn deposit, Bihor County, Romania. Graţianite 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. Graţianite displays weak to modest bireflectance in air and oil, respectively, and strong anisotropy. The mean empirical composition based on 20 electron probe microanalyses is: (Mn0.541Fe0.319Pb0.070Cu0.040Cd0.009 Ag0.001)S0.980(Bi1.975Sb0.018)S1.993(S4.008Se0.012Te0.007)S4.027, corresponding to the ideal formula MnBi2S4. Graţianite crystallizes in the monoclinic system (space group C2/m). 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: a = 12.6774(25) Å, b = 3.9140(8) Å, c = 14.7581(30) Å, b = 115.31(3)°, V = 662.0(2) Å3, 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).
Ciobanu, C. L., Brugger, J., Cook, N. J., Mills, S. J., Elliott, P., Damian, G. S., & Damian, F. (2014). Gratianite, MnBi2S4, a new mineral from the Baita Bihor skarn, Romania. American Mineralogist, 99(5-6), 1163-1170. https://doi.org/10.2138/am.2014.4836