In early mid-infrared observations (c 1970) two prominent dust emission features were discovered. ... Soon after the discovery of the silicate features another feature at about 11.3 microns was discovered in the spectra of some carbon stars, not as wide or as strong as the silicate features but still thought to be due to a solid material. ... less common features: extreme carbon stars, the AlO/silicate complex, the "unidentified infrared" features, unusual silicate features . ...