End-members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas, and the interlayer-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials, and a list of names formerly 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 recommendations presented were approved by the Commission.

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A B S T R A C T :The classification and nomenclature of chlorites have been critically reviewed. A new classification based on the unified projection system of chemical composition has been proposed in which for the first time all trioctahedral, di-trioctahedral and dioctahedral species are included. The chemical composition of chlorites is controlled by the general crystallochemical formula: (R~+R~+rI~)(Si~4 ~Alx)O10(OH)8, where u + y + z = 6, z = (y -x)/2. This is superior to the known formulae for the trioctahedral and dioctahedral chlorites. It has been shown that the chlorite end-member compositions of Bayliss (1975) project in one point of the projection field leaving many end-member compositions unnamed. As they correspond to the names used previously, a proposal is made to restore these names.Chlorites are hydrous aluminosilicates of rather complex chemical composition and structure. They incorporate primarily Mg, AI and Fe, and to lesser extent Cr, Ni, Mn, V, Cu, and Li in the octahedral sheet within the 2 : 1 layer and in the interlayer hydroxide sheet, and exhibit a large substitution of Si by A1.Classifications of trioctahedral chlorites have been made by several authors, and in the modern ones, (those published after 1950) the number of Si atoms per 4 tetrahedral positions has been used as a major classification criterion. The importance of the octahedral substitutions was underestimated. The most recent proposal for chlorite nomenclature is that of Bayliss (1975). He considered the advantages and disadvantages of previous proposals and found several discrepancies, which brought him to an approach consistent with the general recommendations of the Commission on New Minerals and Mineral Names of the International Mineralogical Association to avoid ill-defined names in favour of end-member compositions. According to the proposal of Bayliss (1975), the end-member compositions of trioctahedral chlorites are: clinochlore chamosite nimite pennantiteThis list has been supplemented (Bailey, 1988) by:baileychlore-(ZnsA1)(Si3A1)Olo(OH)8 (see Rule & Radke, 1988).Frequent substitutions in clinochlores widely distributed in nature are of the type MgVtSi ~v ~ AlVrAlrV and are accompanied by minor substitutions of octahedral cations by 9 1990 The Mineralogical Society

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