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Many chloritic minerals in low-grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties, expand slightly upon glycolation ("expandable chlorite") and/or have excess A1 w relative to A1TM, as well as significant Ca, K and Na contents. Chloritic minerals with these properties fill vesicles and interstitial void space in low-grade metabasalt from northern Taiwan and have been studied with a combination of TEM/AEM, EMPA, XRD, and optical microscopy. The chloritic minerals include corrensite, which is an ordered 1:1 mixed-layer chlorite/smectite, and "expandable chlorite", which is shown to be a mixed-layer chlorite/corrensite. Corrensite and some mixed-layer chlorite/corrensite occur as rims of vesicles and other cavities, while later-formed mixed-layer chlorite/corrensite occupies the vesicle cores. The TEM observations show that the mixed-layer chlorite/corrensite has ca. 20%, and the corrensite has ca. 50% expandable smectite-like layers, consistent with XRD observations and with their abnormal optical properties. The AEM analyses show that high Si and Ca contents, high AlVl/A1TM and low FeVl/(Fe+ Mg) vl ratios of "chlorites" are correlated with interstratification of corrensite (or smectite-like) layers in chlorite. The AEM analyses obtained from 200-500 A. thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low AlIV/SiIV and low FeVI/(Fe + Mg) vI, while chlorite has high AlIV/Si~V and high FeW/(Fe + Mg) vl. This implies that the trioctahedral smectite-like component of corrensite has significantly lower AlIV/Si TM and FeVl/(Fe + Mg) w. The ratios of FeVI/(Fe + Mg) vt and AllV/Si TM thus decrease in the order chlorite, corrensite, smectite. The proportions of corrensite (or smectite-like) layers relative to chlorite layers in low-grade rocks are inferred to be controlled principally by Fe/Mg ratio in the fluid or the bulk rock and by temperature. Compositional variations of" chlorites" in low-grade rocks, which appear to correlate with temperature or metamorphic grade, more likely reflect variable proportions of mixed-Offprint requests to: Yen-Hong Shau layered components. The assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases, such as chlorite-corrensite, corrensite-smectite, or chlorite-corrensite-smectite. A model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1:1 ordered mixed-layer chlorite/smectite.

This report embodies recommendations on zeolite nomenclature approved by the International Mineralogical Association, Commission on New Minerals and Mineral Names. In a working definition of a zeolite mineral used for this review, structures containing an interrupted framework of tetrahedra are accepted where other zeolitic properties prevail, and complete substitution by elements other than Si and Al is allowed. Separate species are recognized in topologically distinctive compositional series in which different extra-framework cations are the most abundant in atomic proportions. To name these, the appropriate chemical symbol is attached by a hyphen to the series name as a suffix, except for the names harmotome, pollucite and wairakite in the phillipsite and analcime series. Differences in space-group symmetry and in order-disorder relationships in zeolites having the same topologically distinctive framework do not in general provide adequate grounds for recognition of separate species. Zeolite species are not to be distinguished solely on the ratio Si : Al except for heulandite (Si : Al < 4.0) and clinoptilolite (Si : Al ≥ 4.0). Dehydration, partial hydration, and overhydration are not sufficient grounds for the recognition of separate species of zeolites. Use of the term "ideal formula" should be avoided in referring to a simplified or averaged formula of a zeolite. Newly recognized species in compositional series are as follows: brewsterite-Sr, -Ba, chabazite-Ca, -Na, -K, clinoptilolite-K, -Na, -Ca, dachiardite-Ca, -Na, erionite-Na, -K, -Ca, faujasite-Na, -Ca, -Mg, ferrierite-Mg, -K, -Na, gmelinite-Na, -Ca, -K, heulandite-Ca, -Na, -K, -Sr, levyne-Ca, -Na, paulingite-K, -Ca, phillipsite-Na, -Ca, -K, and stilbite-Ca, -Na. Key references, type locality, origin of name, chemical data, IZA structure-type symbols, space-group symmetry, unit-cell dimensions, and comments on structure are listed for 13 compositional series, 82 accepted zeolite mineral species, and three of doubtful status. Herschelite, leonhardite, svetlozarite, and wellsite are discredited as mineral species names. Obsolete and discredited names are listed.Keywords: zeolite nomenclature, herschelite, leonhardite, svetlozarite, wellsite, brewsterite, chabazite, clinoptilolite, dachiardite, erionite, faujasite, ferrierite, gmelinite, heulandite, levyne, paulingite, phillipsite, stilbite. SOMMAIRECe rapport contient les recommandations à propos de la nomenclature des zéolites, telles qu'approuvées par l'Association minéralogique internationale, commission des nouveaux minéraux et des noms de minéraux. Dans la définition d'une zéolite retenue ici, les structures contenant une trame interrompue de tétraèdres sont acceptées dans les cas où les autres propriétés satisfont les critères de cette famille de minéraux. De plus, il peut y avoir remplacement complet de Si et Al par d'autres éléments. Des espèces distinctes font partie de séries de compositions dont l'agencement topologique est le même, le cation dominant ne faisant pas partie de la trame ...

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