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We present a fit to the spectral energy distribution of OH 127.8+0.0, atypical asymptotic giant branch star with an optically thick circumstellar dustshell. The fit to the dust spectrum is achieved using non-spherical grainsconsisting of metallic iron, amorphous and crystalline silicates and water ice.Previous similar attempts have not resulted in a satisfactory fit to theobserved spectral energy distributions, mainly because of an apparent lack ofopacity in the 3--8 micron region of the spectrum. Non-spherical metallic irongrains provide an identification for the missing source of opacity in thenear-infrared. Using the derived dust composition, we have calculated spectrafor a range of mass-loss rates in order to perform a consistency check bycomparison with other evolved stars. The L-[12 micron] colours of these modelscorrectly predict the mass-loss rate of a sample of AGB stars, strengtheningour conclusion that the metallic iron grains dominate the near-infrared flux.We discuss a formation mechanism for non-spherical metallic iron grains.Comment: 10 pages, 6 figures, accepted for publication by A&

Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron