Ice‐nucleating properties of clay minerals and stony meteorites

The ice‐nucleating properties of clay minerals have been investigated in relation to their crystalline and surface structures. The kaolin minerals, the illites and halloysite are the most effective and important, their threshold temperatures for ice nucleation lying between −9°Cand −12°C. Minerals of the montmorillonite group and related forms are active only below −15°C. The relative contributions which the various clay minerals are likely to make to the ice‐nucleus content of the atmosphere are discussed in relation to their natural abundance, wind‐borne dispersion and particle size. Kaolinite is considered to be the most important source of highly efficient nuclei in confirmation of results obtained earlier by Mason and Maybank (1958). Tests on three new specimens of stony meteorites showed them to be inactive at −17°C.