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A new collection of clay mineral ‘Crystallinity’ Index Standards and revised guidelines for the calibration of Kübler and Árkai indices

  • Laurence N. Warr (a1)
  • Please note a correction has been issued for this article.


A new set of clay mineral ‘Crystallinity’ Index Standards (CIS) is available for improved calibration of the half-peak-width values of the X-ray diffraction 001 illite reflection (the Kübler index) and the 002 chlorite reflection (the Árkai index), two widely used indices for determining the state of prograde diagenesis and low-temperature metamorphism. Calibration using mudrock standards removes the numerical differences between laboratories caused by variations in sample preparation, machine settings and measurement methods, thus avoiding erroneous grade determinations. The number of standards available has been increased to nine. These can be used to obtain Kübler index values for each CIS sample and Árkai index values for upper anchizonal and epizonal samples. The diagenetic and lower anchizonal mudrocks are not suitable for Árkai index measurements due to the absence of chlorite or overlap by the 001 kaolinite reflection. Applying the new Kübler-equivalent upper and lower boundary limits of the anchizone placed at 0.32°2θ and 0.52°2θ, respectively (Warr & Ferreiro Mählmann, 2015), the nine standards from the Palaeozoic mudrocks of southwest England now comprise two diagenetic, two lower anchizonal, three upper anchizonal and two epizonal grade samples. These range from weakly cleaved mudstones to strongly foliated slates.


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This paper was presented during the session: ‘GG01 – Clays in faults and fractures + MI-03 – Clay mineral reaction progress in very low-grade temperature petrologic studies’ of the International Clay Conference 2017.

Guest Associate Editor: S. Potel



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Árkai, P. (1991) Chlorite crystallinity: an empirical approach and correlation with illite crystallinity, coal rank and mineral facies as exemplified by Palaeozoic and Mesozoic rocks of northeast Hungary. Journal of Metamorphic Geology, 9, 723734.
Blenkinsop, T.G. (1988) Definition of low-grade metamorphic zones using illite crystallinity. Journal of Metamorphic Geology, 6, 623636.
Drits, V.A., Eberl, D.D. & Środoń, J. (1998) XRD measurement of mean thickness, thickness distribution and strain for illite and illite–smectite crystallites by the Bertaut–Warren–Averbach technique. Clays and Clay Minerals, 46, 3850.
Eberl, D.D. & Velde, B. (1989) Beyond the Kübler index. Clay Minerals, 24, 571577.
Ferreiro Mählmann, R. & Frey, M. (2012) Standardization, calibration and correlation of the Kübler-index and the vitrinite/bituminite reflection: an inter-laboratory and field related study. Swiss Journal of Geoscience, 105, 153170.
Frey, M. (1987) Very low-grade metamorphism of clastic sedimentary rocks. Pp. 958 in: Low Temperature Metamorphism (Frey, M., editor). Blackie and Son Ltd, Glasgow, UK.
Guggenheim, S., Bain, D.C., Bergaya, F., Brigatti, M.F., Drits, D.D., Eberl, D.D., Formoso, M.L.L., Galán, E., Merriman, R.J., Peacor, D.R., Stanjek, H. & Watanabe, T. (2002) Report of the Association Internationale pour l'Etude des Argiles (AIPEA) Nomenclature Committee for 2001: order, disorder and crystallinity in phyllosilicates and the use of the ‘crystallinity index’. Clay Minerals, 37, 389393.
Kübler, B. (1967) La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. Pp. 105121 in: Étages Tectoniques. Colloque de Neuchâtel 1966, A La Baconnière, Neuchâtel, Switzerland.
Kübler, B. (1968) Evaluation quantitative du métamorphisme par la cristallinité d l'illite. Bulletin du Centre de recherches, Pau – S.N.P.A., 2, 385397.
Kübler, B. (1984) Les indicateurs des transformations physiques et chimiques dans la diagenèse, température et calorimétrie. Pp. 489596 in: Thermobarométrie et Barométrie Géologiques (Lagache, M., editor). Bulletin de la Société Française de Minéralogie et de Cristallographie, Paris, France.
Kisch, H.J. (1990) Calibration of the anchizone: a critical comparison of illite ‘crystallinity’ scales used for definition. Journal of Metamorphic Geology, 8, 3146.
Kisch, H.J. (1991) Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings, and interlaboratory samples. Journal of Metamorphic Geology, 9, 665670.
Kisch, H.J., Árkai, P. & Brime, C. (2004) On the calibration of the Kübler index (illite ‘crystallinity’). Schweizerische Mineralogische und Petrographische Mitteilungen, 84, 323–33.
Krumm, S. & Buggisch, W. (1991) Sample preparation effects on illite crystallinity measurement: grain size gradation and particle orientation. Journal of Metamorphic Geology, 9, 671677.
Merriman, R.J. & Frey, M. (1999) Patterns of very low-grade metamorphism in metapelite rocks. Pp. 61107 in: Low-Grade Metamorphism (Frey, M. & Robinson, R., editors), Blackwell Science, Oxford, UK.
Warr, L.N. (2014) 20 years of the Crystallinity Index Standard: a progress report. MECC 2014 conference abstract, Dresden, Germany. URL
Warr, L.N. (1996) Standardized clay mineral crystallinity data from the very low-grade metamorphic facies of southern New Zealand. European Journal of Mineralogy, 8, 115127.
Warr, L.N. & Cox, S.C. (2016) Correlating illite (Kübler) and chlorite (Árkai) ‘crystallinity’ indices with metamorphic mineral zones of the South Island, New Zealand. Applied Clay Science, 134, 164174.
Warr, L.N. & Ferreiro Mählmann, R. (2015) Recommendations for Kübler index standardization. Clay Minerals, 50, 283286.
Warr, L.N. & Nieto, F. (1998) Crystallite thickness and defect density of phyllosilicates in low-temperature metamorphic pelites; a TEM and XRD study of clay-mineral crystallinity index standard. The Canadian Mineralogist, 36, 14531474.
Warr, L.N. & Rice, A.H.N. (1994) Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology, 12, 141152.


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A new collection of clay mineral ‘Crystallinity’ Index Standards and revised guidelines for the calibration of Kübler and Árkai indices

  • Laurence N. Warr (a1)
  • Please note a correction has been issued for this article.


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