American Minetralogist, Volume 65, pages 1-7, 1980 Summary of recommendations of AIPEA nomenclature committee on clay minerals S. W. BAILEY, CHAIRMAN1 Department of Geology and Geophysics University of Wisconsin-Madison Madi~on, Wisconsin 53706 Introduction This summary of the recommendations made to Because of their small particle sizes and v~riable date by the international nomenclature committees degrees of crystal perfection, it is not surprisi4g that has been prepared in order to achieve wider dissemi- clay minerals proved extremely difficult to character- nation of the decisions reached and to aid clay scien- ize adequately prior to the development of ~odem tists in the correct usage of clay nomenclature. Some analytical techniques. Problems in charactetization of the material in the present summary has been led quite naturally to problems in nomenclatute, un- taken from an earlier summary by Bailey et al. doubtedly more so than for the macroscopic~ more (1971a). crystalline minerals. The popular adoption ~ the early 1950s of the X-ray powder diffractometer for Classification . clay studies helped to solve some of the probl ms of Agreement was reached early in the international identification. Improvements in electron micro copy, discussions that a sound nomenclatur~ is necessarily electron diffraction and oblique texture electr ;n dif- based on a satisfactory classification scheme. For this fraction, infrared and DT A equipment, the de elop- reason, the earliest and most extensive efforts of the ment of nuclear and isotope technology, of high- several national nomenclature committees have been speed electronic computers, of Mossbauer spec rome- expended on classification schemes. Existing schemes ters, and most recently of the electron micr probe were collated and discussed (see Brown, 1955, Mac- and scanning electron microscope all have ai ed in kenzie, 1959, and Pedro, 1967, for examples), sym- the accumulation of factual information on clays. posia were held at national meetings, and polls were This, in turn, should facilitate eventual agreem nt on taken of clay scientists in 32 countries as to their the nomenclature of clays. preferences. Armed with these data, the international Probably the earliest attempt by clay scient sts fo representatives have been able to agree upon most reach agreement on nomenclature and classifi ation features of a broadly based scheme for the phyllosill- on an international basis was at the Interna ional . cates as a whole (Mackenzie, 1965a,b; Brindley, Soil Congress held in Amsterdam in 1950 (B dley 1967). et al., 1951). Since that time national Nomenc ature Table 1 gives the classification scheme in its pres- Committees have been established in many oun- ent form. The phyllosilicates are divided into groups, tries. Recommendations from these national roups each containing dioctahedral and trioctahedral sub- have been considered every three years at the nter- groups. Each sub-group in turn is divided into min- national Clay Conferences, first by the Nomenc ature eral species. This subdivision corresponds to succes- Sub-Committee of CIPEA(Comite Internationa Pour sive stages of refinement in the identification process. l'Etude des Argiles) and since 1966 by the N men- It is anticipated that the precise definitions of the clature Committee of AIPEA (Association nter- groups and sub-groups and their names will evolve . nationale Pour l'Etude des Argiles). These ter- and change with time. This table differs from pre- national committees in turn have worked closel with viously published versions in two respects. Smectite the Commission on New Minerals and M.neral has now been accepted as the group name for clay N ames of the IMA (International Mineralogic 1 As- minerals with. layer charge between 0.2. and 0.6 per sociation). formula unit. This decision, made at the 1975 Mexico City meeting (Brindley and Pedro, 1976), was based Ifor the AIPEA Nomenclature Committee: A. Alietti (Ita y), G. on increased usage world-wide of this name rather W. Brindley (U.S.A.), M. L. L. Formosa (Brazil), K. Jasm nd (F. R. Germany), J. Konta (Czechoslovakia), R. C. Mac enzie than of the alternate dual name of montmorillonite- (U.K.), K. Nagasawa (Japan), R. A. Rausell-Colom (Spa. ), and saponite for the group. Dual names still exist for the B. B. Zvyagin (U.S.S.R.). kaolinite-serpentine and pyrophyllite-talc groups. 0003-004X/80/0 102-000 1$02.00 I ---~-- 2 BAILEY: AIPEA NOMENCLATURE COMMITTEE Table 1. Classification scheme for phyllosilicates related to clay minerals Group Layer (x=charge per Type f-;rmula unit) Subgroup Species* 1:1 Kaolinite-serpentine Kaolinite Kaolinite, dickite, halloysite x 'V 0 Serpentine Chrysotile, lizardite, amesite Pyrophyllite-ta1c Pyrophyllite Pyrophy11ite x 'V 0 Talc Talc Smectite Dioctahedra1 smectite Montmorillonite, beidellite x 'V 0.2-0.6 Trioctahedral smectite Saponite, hectorite, sauconite Vermiculite Dioctahedra1 vermiculite Dioctahedra1 vermiculite ~ 'V 0.6-0.9 Trioctahedra1 vermiculite Trioctahedral vermiculite 2:1 Micall Dioctahedra1 mica Muscovite, paragonite x 'V 1 Trioctahedral mica Ph10gopite, biotite, lepidolite Brittle mica Dioctahedral brittle mica Margarite x 'V 2 Trioctahedral brittle mica C1intonite, anandite Chlorite Dioctahedra1 chlorite Donbassite x variable Di:trioctahedra1 chlorite Cookeite, sudoite Trioctahedra1 chlorite Clinochlore, chamosite, nimite *On1y a few examples are given #The status of illite (or hydromica), sericite, 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 maybe interstratified. Suggested names of kandite and septechlorite for the terlayer bonding or of certain resultant physical kaolin and serpentine minerals, respectively, have properties. Thus, it does not require a category of not been approved by the AIPEA Committee, and "pseudo-layer silicates" for minerals, such as paly- should not be used. The second change is to treat gorskite and sepiolite, that do not possess marked chlorite as consisting of a 2: 1 layer plus an interlayer basal cleavages. The criterion of a continuous tet- hydroxide sheet, rather than as a 2: 1: 1 or 2: 2 layer rahedral sheet does exclude "quasi-layer silicates," type. This emphasizes the similarity of chlorite to such as astrophyllite, lamprophyllite, bafertisite, and other clay minerals containing interlayer material haradaite, in which 5-fold or 6-fold coordinated (Brindley and Pedro, 1972). groups interrupt the continuity of the tetrahedral net. Definition of phyllosiUcate Standardization of structural terms Table 1 assumes a specific definition of a phyllo- At the 1975 Mexico City meeting the AIPEA N 0- silicate (or layer silicate). This definition was dis- menclature Committee noted that "lattice" and cussed most recently at the AIPEA Nomenclature "structure" continue to be misused by authors and Committee meeting held in Madrid in 1972, at which speakers. A "lattice" is not synonymous with "struc- a 1969 definition was modified. The present defini- ture," but is a uniform distribution of points in space tion (Brindley and Pedro, 1972) states "Clay minerals (e.g. the 14 Bravais lattices). The terms "layer lattice" belong to the family of phyllosilicates and contain and "Schichtgitter" are incorrect and should not be continuous two-dimensional tetrahedral sheets of used. Layer structure, layer silicate, and phyllosili- composition T 205 (T = Si, AI, Be, ...) with tetrahedra cate are acceptable terms (Brindley, 1967; Brindley linked by sharing three comers of each, and with the and Pedro, 1976). fourth comer pointing in any direction. The tetrahe- In 1972 the Committee agreed upon usage of the dral sheets are linked in the unit structure to octahe- terms "plane," "sheet," "layer," "unit structure," and dral sheets, or to groups of coordinated cations, or in- their equivalents in other languages (Brindley and dividual cations." The present definition is based on PedrQ, 1972). Recommended usage is as a single the nature of the silicate parts of the structure, and plane of atoms, a tetrahedral or octahedral sheet, and does not include previous requirements of weaker in- a 1: 1 . or 2: 1 layer. Thus, plane, sheet, and layer refer BAILEY: AIPEA NOMENCLATURE COMMITTEE 3 Table 2. Structural terms of reference and their equivalents in different languages Spanish English French German . Russian Italian plane plan Ebene ITJIOCKOCTb plano plano sheet couche Schicht CETKA capa strato layer feuillet Schichtpaket OJIOIll estrato 0 pacchet to paquete (de capas) interlayer espace Zwischenschicht MEJKOJIOEBOW material interlaminar inters trato interfoliaire nPOMEJKYTOK (Me)l(cnoi-i) unit structure unite structurale Struktur Einheit ITAKET unidad estructural unita strutturale to increasingly thicker arrangements. A sheet is a (2) "In general, polytypes should not receive indi- combination of planes and a layer is a combination vidual mineral names. Instead, a set of related poly- of sheets. In addition, layers may be separated from types should be designated by a single name followed one another by various interlayer materials, including by a structural symbol suffix that defines the layer cations, hydrated cations, organic molecules, and hy- stacking differences." A recommended system of droxide octahedral groups and sheets. The total as- structural symbols is described in the report. sembly of a layer plus interlayer material is referred (3) "Polytype mineral names already in existence to as a unit structure. Table 2