IT has been suggested1 that the interstellar extinction might be explained by assuming that the interstellar dust is composed of an appropriate size distribution of diamond particles. The imaginary part of the index of refraction of diamond increases sharply from near zero to about 1.0 at λ−1 = 5.0 µm−1, giving an albedo near unity in the visible and strong extinction in the ultraviolet, as required by recent observations.