  We present a Spitzer Space Telescope spectroscopic study of a sample of 25
planetary nebulae in the Magellanic Clouds. The low-resolution modules are used
to analyze the dust features present in the infrared spectra. This study
complements a previous work by the same authors where the same sample was
analyzed in terms of neon and sulfur abundances. Over half of the objects (14)
show emission of polycyclic aromatic hydrocarbons, typical of carbon-rich dust
environments. We compare the hydrocarbon emission in our objects to those of
Galactic HII regions and planetary nebulae, and LMC/SMC HII regions. Amorphous
silicates are seen in just two objects, enforcing the now well-known-fact that
oxygen-rich dust is less common at low metallicities. Besides these common
features, some planetary nebulae show very unusual dust. Nine objects show a
strong silicon carbide feature at 11um and twelve of them show magnesium
sulfide emission starting at 25um. The high percentage of spectra with silicon
carbide in the Magellanic Clouds is not common. Two objects show a broad band
which may be attributed to hydrogenated amorphous carbon and weak
low-excitation atomic lines. It is likely that these nebulae are very young.
The spectra of the remaining eight nebulae are dominated by the emission of
fine-structure lines with a weak continuum due to thermal emission of dust,
although in a few cases the S/N in the spectra is low, and weak dust features
may not have been detected.
