LAUSR

Abstract We experimentally measure the mid-IR spectra of half-millimeter-sized olivine particles with very compact morphology and smooth surfaces. We find that the 10-μm silicate feature is present in these large, irregularly shaped samples having surface roughness that is much smaller than optical wavelengths. Based on Mie theory, which assumes the particles are spherical, this feature should not exist for such large particles. As a consequence, its presence has been taken as an indicator that the particles or grains composing such particles were micron-sized or smaller. The measurement of this feature in real, irregularly shaped particles, suggests that the assumption of sphericity may severely limit our interpretations of remote-sensing data.