PAH's and Crystalline Silicates in Planetary Nebulae

An overview is given of the PAH and crystalline silicate emissions seen in the SWS guaranteed-time programme on planetary nebulae. Of the 9 objects on which good continuum measurements were obtained above 29 µm, 7 show evidence of olivine emission at 33.5 µm. PAH emission is seen in 5 of these objects, 3 objects show both PAH's and olivines. The presence of both types of features in a single object points to separate carbon-rich and oxygen-rich episodes of mass ejection. The spectrum of the nebula NGC 6302 shows a wealth of features in the range between 20 and 45 µm, many of which can be identified with olivines or pyroxenes.