NOMENCLATURE OF THE MICAS

End-members and species, defined with permissible ranges of compositio n, are presented for the true micas, the brittle micas, and the interl ayer-deficient micas. The determination of the crystallochemical formu la for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual che mical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials, and a list of names forme rly or erroneously used for micas are presented. The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The definitions and recom mendations presented were approved by the Commission.