Extinction values for SiC particles obtained in the laboratory by various authors are compared with low-dispersion spectra of M-Mira variables taken by IRAS. The excesses in λ 12 μm and λ 20 μm described by Vardya et al. (1986, Ap.J. Lett. 304, L29), correspond to SiC particle emission of different sizes, which might be related to the shock wave intensities in the atmospheres of these stars.