Standardisation of polytype suffixes

Abstract

The Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association has published guidelines on a number of matters dealing with mineralogical nomenclature, including polytype nomenclature (e.g. Nickel and Mandarino, 1987). In essence, polytypes are distinguished by alphanumeric symbols appended to the root name and joined to it by a hyphen. The numeric part of the symbol represents the layering periodicity, and the alphabetic part, rendered in italic print, represents the crystallographic system. For example, wurtzite 4H is a hexagonal wurtzite polytype with a periodicity of 4 times the c-dimension of the wurtzite parent. Prior to the publication of these guidelines, various other polytype symbols had been used in the mineralogical literature and, in an effort to standardise polytype nomenclature, members of the CNMMN decided that previous usage should be brought into conformity with current practice, which follows recommendations of the International Union of Crystallography (Guinier et al., 1984). Polytype names in the literature that require changing are as follows: