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This paper reports the results obtained in a study of the crystal structure of two villamaninite samples from Villamanin (Le6n, Spain), labeled (1) and (2). Villamaninite, (Cu,Ni,Co,Fe)(S,Se)2, is a pyrite-type disulfide. Different long-period elements, including Au, in ionic substitution are also observed. Previous authors have assumed a cubic Pa3 symmetry for this mineral. The result of our single crystal study shows a deviation from the cubic symmetry Pa3 pyrite-type to a pseudocubic symmetry, which is in agreement with the observed optical anisotropy shown by both samples. The structural refinement process leads to a monoclinic model, space group P1211, with a-5.709 (2), b--5.707(2), c=5.708(2)A, 3=90.01(1) ° for sample (1),° and a = 5.704 (3), b -5.703 (3), c-5.704(3)A, 3 = 89.99(2) ° for sample (2), with Z-4. Previous M6ssbauer spectroscopic studies stating two different cation sites for Au support the monoclinic model. Acta Cr)'stallographic'a Section B

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