Pyrite with lower cubic symmetry from Lavrion, Greece

In this study, we examined the morphological, chemical, and structural details of tetrahedral pyrite crystals from the Jean Baptiste mine in Lavrion, Greece. Pyrite occurs in three generations. Tetrahedral crystals of the first generation are left- or right-handed with the lowest cubic 23 symmetry. In this generation, there are twins with higher cubic m_3 and hexagonal 6 symmetry. All crystals of the second generation are primarily interpenetrated into twins with a cubic _4m3 symmetry. Some, however, continue to twin up to crystals with the highest cubic m_3m and hexagonal 6mm symmetry. Third-generation crystals overgrow second-generation crystals in a non-oriented manner. Chemical analysis confirms chemically pure pyrite, and single-crystal X-ray analysis of the first- and the second-generation crystals confirms the pyrite-specific m__3 symmetry. The morphology of the single crystals and twins indicates that first generation of single pyrite crystals should have the lowest cubic 23 symmetry, which is not confirmed by the structural analysis. This discrepancy may be due to changed pT conditions and the consequent transformation of the original pyrite structure with symmetry 23 into a secondary structure with m__3 symmetry, or to suboptimal conditions in determining the structure by X-ray diffraction.