Canadian Mineralogist Vol. 18, pp. 143-150, (1980) SUMMARY OF RECOMMENDATIONS OF THE AIPEA NOMENCLATURE COMMITIEE S. W. BAILEY, Chairman· Department of Geology and Geophysics, University of Wisconsin - Madison, Madison,. Wisconsin 53706, U.s.A. INTRODUCTION turn have worked closely with the Commission' on New Minerals and Mineral Names of the Because of their small particle-size and vari­ I.M.A. (International Mineralogical Association). able degree of c'rystal perfection, it is not sur­ This summary of the recommendations made prising that clay minerals proved extremely to date by the international nomenclature-com­ difficult to characterize adequately prior to the mittees has been prepared in order to dissemi­ development of modern analytical,techniques. nate more widely the decisions reached and to Problems in characterization led quite naturally aid clay scientists in the correct usage of clay to problems in nomenclature, undoubtedly more nomenclature. Some of the material in the so than for the macroscopic, more perfectly present summary has been taken from an earlier crystalline minerals. The popular adoption in summary by Bailey et al. (1971a). the early 19508 of the powder X-ray diffracto­ meter for clay studies helped to solve some of CLASSIFICATION the problems of identification. Improvements in electron microscopy, electron diffraction and Agreement was reached early in the inter­ oblique texture electron diffraction, infrared and national discussions that a sound nomenclature DTA equipment, plus the development of nu­ is necessarily based on a satisfactory classifica­ clear and isotope technology, high-speed elec­ tion scheme. For this reason, the earliest and tronic computers, Mossbauer spectrometers and most extensive efforts of the several national most recently, the electron microprobe and committees on nomenclature have been ex­ scanning electron-microscope all have aided in pended on classification schemes. Existing the accumulation of factual information on schemes were collated and discussed (e.g., clays. This, in turn, should facilitate eventual Brown 1955 Mackenzie 1959, Pedro 1967), agreement on the nomenclature of clays. symposia we~e held at national meetings, and Probably the earliest attempt by clay scientists polls were taken of clay scientists in ~2 coun­ to reach agreement on nomenclature and classi­ tries as to their preferences. Armed With these fication on an international basis occurred at data the international representatives have been the International Soil Congress held in Amster­ able'to agree upon most features of a broadly dam in 1950 (Brindley et al. 1951). Since that based scheme for the phyllosilicates as a whole time national Nomenclature Committees have (Mackenzie 1965a,b, Brlndley 1967). been established in many countries. Recom­ Table 1 gives the classification sche~~ in mendations from these national groups have its present form. The phyllosilicates are diVided been considered every three years at the Inter­ into groups, each containing dioctahedr.al and national Clay Conference, first by the Nomen­ trioctahedral subgroups. Each sub~oup l~ .t~rn clature Subcommittee of CIPEA (Comite Inter­ is divided into mineral species. This subdLvlslon national pour l'Etude des Argiles) and since corresponds to successive stages ~f ref~n~ment 1966 by the Nomenclature Committee of in the identification process. It IS antICipated AIPEA (Association Internationale pour l'Etude that the precise definitions of t~e groups and des Argiles). These international committees in subgroups and their names will evolve and change with time. This. tabl.e differs from •for the AIPEA (Association Internationale pour previously published verSIons 10 two respects. l'Etude des Argiles) Nomenclature Committee: A. Smectite has now been accepted as the group Alieni (Italy), G. W. Brindley (U.S.A.), M. L. L. name for clay minerals with layer. char~e be­ Formosa (Brazil), K. Jasmund (F.R.G.), J. Konta tween 0.2 and 0.6 per formula urut. This de­ (Czechoslovakia), R. C. Mackenzie (U.K.), K. Nagasawa (Japan), R. A. Rausell-Colom (Spain) cision, made at the 1975 Mexico City meeting and B. B. Zvyagin (U.S.S.R.). (Brindley & Pedro 1976), was based on an 143 144 THE CANADIAN MINERALOGIST TABLE 1. CLASSIFICATION SCHEME FOR PHYLLOSILICATES RELATED TO CLAY MINERALS Group Layer ("aeharge per Type fonnula unit) Subgroup Species· 1,1 Kaollnlte-serpentlne Kaollnlte Kaollnfte, dickfte, hanoyslte " '" 0 Serpentl ne Chrysotlle, lfzardlte, erneslte Pyrophylllte-tal c Pyrophyll Ite Pyrophyll fte Talc Talc " '" 0 SIrectfte 010ctahedral smectfte Montmorlllonlte, beldelllte " '" 0.2-0.6 Trloctahedral smectfte saponite, hectorite. sauconfte Vennlcullte Oloctahedral vennlcullte Oloctahedral vennl cuI Ite " '" 0.6-0.9 Trloctahedral vennl cuI fte Trloctahedral vennl cul lte 2:1 Mica' Oloctahedral ml ca Muscovite, paragonite "", 1 Trloctahedral mlca Phlogopfte, blotlte, lepldolfte Brittle mica Oloctahedral brittle mica Marg.rlte ,,"'2 Trloctahedral brittle mica Cl I ntonl te, anandl te Chlorfte Oloctahedral chlorfte Oonbasslte " variable Ol,trloctahedral chlorlte Cookel te, sudol te Trloctahedral chlorfte Cllnochlore, chomoslte, nlmlte • Only a few examples are given. , The status of I1lfte (or hydromlca), serlcfte, etc. must be left open at present, because It Is not clear whether or at what level they would enter the table: many materials so designated may be Interstratlfled. increased world-wide usage of this name as cal properties. Thus, it does not require a opposed to the alternate dual name montmo­ category of "pseudolayer silicates" for minerals rillonite-saponite for the group. Dual names such as palygorskite and sepiolite that do not still exist for the kaolinite-serpentine and pyro­ possess marked basal cleavages. The criterion phyllite-talc groups. Suggested names of kandite of a continuous tetrahedral sheet does exclude I and septechlorite for the kaolin and serpentine "quasilayer silicates" such as astrophyllite, lam­ minerals, respectively, have not been approved prophyllite, bafertisite and haradaite, in which by the AIPEA Committee and shoUld not be 5- or 6-fold coordinated groups interrupt the used. The second change is to treat chlorlte as continuity of the tetrahedral net. consisting of a 2: 1 layer plus an interlayer hydroxide sheet, rather than as a 2: 1: I .or 2:2 STANDARDIZATION OF STRUCTURAL TERMS layer type. This emphasizes the similarity of chlorite with other clay minerals containing At the 1975 Mexico City meeting the AIPEA interlayer material (Brindley & Pedro 1972). Nomenclature Committee noted that lattice and structure continue to be misused by authors and DEFINITION OF PHYLLOSILICATE speakers. A lattice is not synonymous with structure; it is a uniform distribution of points Table 1 assumes a specific definition of a in space (e.g., the 14 Bravais lattices). The terms. phyllosilicate (or layer silicate). This definition "layer lattice" and "Schichtgitter" are incorrect was discussed most recently at the AIPEA No­ and should not be used. Layer structure, layer menclature Committee meeting held in Madrid silicate and phyllosilicate are acceptable terms in 1972, at which a 1969 definition was modi­ (Brindley 1967, Brindley & Pedro 1976). fied. The present definition (Brindley & Pedro In 1972 the Committee agreed upon usage 1972) states: "Clay minerals belong to the of the terms plane, sheet, layer, unit structure family of phyllosilicates and contain contin­ and their equivalents in other languages (Brind­ uous two-dimensional tetrahedral sheets of com­ ley & Pedro 1972). Recommended usage of position TgOs (T = Si, Al, Be, ...) with tetra­ these is: a single plane of atoms, a tetrahedral hedra linked by sharing three corners of each, or octahedral sheet and a 1:1 or 2:1 layer. Thus, and with the fourth corner pointing in any di­ plane, sheet and layer refer to increasingly rection. The tetrahedral sheets are linked in the thicker arrangements. A sheet is a combination unit ;ltructure to octahedral sheets, or to groups of planes and a layer is a combination of sheets. of coordinated cations, or individual cations." In addition, layers may be separated from one The present definition is based on the nature another by various interlayer materials, includ-. of the silicate parts of the structure, and does ing cations, hydrated cations, organic molecules not include previous requirements of weaker and hydroxide octahedral groups and sheets. interlayer bonding or of certain resultant physi- The total assembly of a layer plus interlayer AIPEA NOMENCLATURE RECOMMENDATIONS 145 'TABLE 2. STRUCTURAL TERMS OF REFERENCE AND THEIR EQUIVALENTS IN DIFFERENT LANGUAGES Engl1sh French German Russ1an Span1 sh Ital1an plane plan Ebene l1JJOCl<OCTb pIano pIano sheet couche Sch1cht OOTKB, capa strato layer feu111et Sch1 chtpaket cm!! estrato 0 pacchetto paquete (de capas) 1nterlayer espace Zw1 schensch1 cht MI31KCJlD8BO mater1al 1nterlam1nar interstrato 1nterfol1a1re ~K (MelKCJlOi1) un1t structure unit~ structurale Struktur E1nheit llllKeT un1 dad estructuraI unita strutturale material is referred to as a unit structure. suffix that defines the layer stacking differ­ Table 2 lists the equivalent terms in other ences." A recommended system of structural languages, as modified at the 1978 Oxford symbols is described in the report. meeting. 3. "Polytype mineral names already in ex­ The terms "talc layer" and "brucite sheet" istence that have international acceptance and are not suitable descriptions of the component serve a useful