  The flattening of the 10mu silicate emission feature observed in the spectra
of T Tauri and Herbig Ae/Be stars is usually interpreted as an indicator of
grain growth. We show in this paper that a similar behaviour of the feature
shape occurs when the porosity of composite grains varies. The fluffy
aggregates, having inclusions of different sizes, were modeled by multi-layered
spheres consisting of amorphous carbon, amorphous silicate and vacuum. It is
also found that the inclusion of crystalline silicates in composite porous
particles can lead to a shift of the known resonances and production of new
ones.
