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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’

¹ Chairman, AIPEA Nomenclature Committee, Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago, Illinois 60607, USA, ² Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, UK, ³ Centre de Recherche de la Matière Divisée (CRMD), National Centre of Scientific Research, University of Orléans, 1b Rue de la Férollerie, 45 071 Orléans Cedex 2, France, ⁴ Department of Earth Sciences, Modena and Reggio Emilia University, Largo S. Eufemia 19, I-41100, Modena, Italy, ⁵ Geological Institute of the Russian Academy of Science, 7 Pyzerskii Per, Moscow J-17 Russia, ⁶ (Guest Member), US Geological Survey, 3215 Marine St., Boulder, Colorado 80303, USA, ⁷ 9500, Ave Bento Gonçalves, Campus do Vale, Institute of Geosciences, University Federal do Rio Grande do Sul, Porto Alegre - RS - Brazil, CEP - 91540-000, ⁸ Department of Crystallography and Minerals, Facultad de Quimica Universite, Sevilla, Spain, ⁹ (Guest Member), British Geological Survey, Keyworth, Nottingham NG12 5GG, UK, ¹⁰ (Guest Member), Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA, ¹¹ Lehrstuhl für Bodenkunde, Technische Universtät Munchen, D-85350 Freising-Weihenstephan, Germany and ¹² Joetsu University of Education, Joetsu Niigata 943, Japan

^* E-mail: xtal@uic.edu

(Received 3 January 2002; KEYWORDS: amorphous, Árkai index, crystallinity, Crystallinity Index, disorder, electron amorphous, Hinckley index, Kübler index, near amorphous, nomenclature, order, X-ray amorphous

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
The purpose of this report is to describe the appropriate use of indices relating to crystallinity, such as the ‘crystallinity index’, the ‘Hinckley index’, the ‘Kübler index’, and the ‘Árkai index’. A ‘crystalline’ solid is defined as a solid consisting of atoms, ions, or molecules packed together in a periodic arrangement. A ‘crystallinity index’ is purported to be a measure of crystallinity, although there is uncertainty about what this means (see below). This report discusses briefly the nature of order, disorder and crystallinity in phyllosilicates and discusses why the use of a ‘crystallinity index’ should be avoided. If possible, it is suggested that indices be referred to using the name of the author who originally described the parameter, as in ‘Hinckley index’ or ‘Kübler index’, or in honour of a researcher who investigated the importance of the parameter extensively, as in ‘Árkai index’.

In contrast to a crystalline solid, an ‘amorphous’ solid is one in which the constituent components are arranged randomly. However, many variations occur between the two extremes of crystalline vs. amorphous. For example, one type of amorphous material might consist simply of atoms showing no order and no periodicity. Alternatively, another amorphous material may consist of atoms arranged, for example, as groups of tetrahedra (i.e. limited order) with each group displaced or rotated (e.g. without periodicity) relative to another. Thus, this latter material is nearly entirely amorphous, but differs from the first. Likewise, disturbance of order and periodicity may occur in crystalline materials. The terms ‘order’ and ‘disorder’ refer to the collective nature or degree of such disturbances. Although seemingly simple notions, ‘crystalline’ and ‘amorphous’ are complex concepts.

Crystalline substances may show a periodic internal structure based on direction. For example, two-dimensional periodicity is common in phyllosilicates where two adjacent sheets or layers must mesh. For example, . . . [Full Text of this Article]

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