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A random, hydrogen‐free, assembly of microscopic sp 2  carbon chips, forming a macroscopically homogeneous and isotropic solid, is proposed as a model carrier for the ultraviolet (UV) interstellar extinction band. The validity of this model is based on the calculation of the Bruggeman average dielectric function of a mixture of the known parallel and perpendicular dielectric functions of graphite. The π absorption feature of Rayleigh‐sized spheres of this mixture falls near  4.6 μm −1   (2175 Å), but its width is  1.5 μm −1  , somewhat larger than the astronomically observed average,  1 μm −1  . This is confirmed by measurements of the reflectance of an industrial material, polycrystalline graphite. A better fit to the interstellar feature position and width is obtained with a hypothetical material, having the same dielectric functions as natural graphite, except for less extended wings of the π resonance. Physically, this could result from changes in the electronic band structure due to previous thermal histories. In this model, the Frölich feature central wavelength depends only on the π resonance frequency, while its width depends only on the damping constant of the same resonance. This explains the range of observed feature widths at constant feature wavelength.

A polycrystalline graphite model for the 2175 Å interstellar extinction band