Room-temperature Mössbauer spectra have been measured for icosahedral (i-phase) ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Fe}}_{15}$ and iron-doped decagonal (T-phase) ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{15}$${\mathrm{Co}}_{20}$ quasicrystals. The observed T-phase spectrum is qualitatively different from any other known quasicrystal, and unquestionably demonstrates the presence of two quite separate distributions of iron sites in this phase. The results are interpreted in terms of an atomically decorated, prismatic Penrose-tile model of sufficient generality to cover a wide range both of binary and of ternary T-phase compositions. This same model is used to account for the absence of the ‘‘two-site’’ form of Mössbauer spectrum in T-phase Al-Mn compositions and to interpret the local structural features of T phases (as determined by extended x-ray-absorption fine structure) and their possible relationship to local i-phase environments.

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