Interstellar extinction by quartz grains

Abstract

Knacke has pointed out that quartz particles possess strong absorption bands at λ ~ 10μ. Although these features occur in the spectral region 3-10μ, where Johnson has found humps in interstellar extinction curves, by itself this cannot be taken as indicating a silica component in the interstellar grains. It has already been pointed out that impurities in any solid with a Debye frequency close to that of graphite would give optically active lattice bands at λ~10μ^∗. Further evidence would be necessary before quartz could be considered as a serious alternative to interstellar graphite grains.