Abstract: EXAFS and Mössbauer data on synthetic silver-rich tetrahedrite, (Cu, Ag)_10+xFe_2−xSb₄S₁₃, reveal the presence of Fe²⁺ and Fe³⁺ the former occupying trigonal planar sites and the latter tetrahedral sites. There is also a clear relationship between increased silver substitution and an increase in Fe²⁺. The amount of Fe³⁺ incorporated in the synthetic tetrahedrites is proportional to the excess of Cu⁺ (Cu + Ag > 10 atoms) in the mineral, thus maintaining a charge balance. The iron in the natural tetrahedrites and the tennantite examined is mainly tetrahedrally co-ordinated Fe²⁺.