Spectroscopic observations at 2.4 - 45 microns of the young supernova remnant Cas A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS) reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are observed at high velocities (several thousand km/s), and are therefore associated with the supernova ejecta known as the fast-moving knots (FMKs). Continuum emission from dust is also seen in the Cas A spectrum. The continuum strength is spatially well correlated

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... the O and Ar line strengths, indicating that the dust emission also arises from the FMKs. The dust continuum has an emission feature at ~22 microns which cannot be fit by typical astronomical silicates, but can be fit with a particular class of silicate minerals. This suggests that the dust in Cas A is silicate material that has freshly condensed from the Cas A ejecta into a mineral form that is uncharacteristic of typical ISM dust grains.