Report of the Association International Pour l'Étude des Argiles (AIPEA) nomenclature committee for 2001; order, disorder and crystallinity in phyllosilicates and the use of the "crystallinity index"

• Published in: Clays and clay minerals Vol. 50; no. 3; pp. 406 - 409
• Main Authors: Guggenheim, Stephen, Bain, Derek C, Bergaya, Faiza, Brigatti, Maria F, Drits, Victor A, Eberl, Dennis D, Formoso, Milton L. L, Galan, Emilio, Merriman, Richard J, Peacor, Donald R, Stanjek, Helge, Watanabe, Takashi
• Format: Journal Article
• Language: English
• Published: Clay Minerals Society 01.06.2002
• Subjects: amorphous materials; Arkai index; clay mineralogy; clay minerals; crystallinity; Hinckley index; Kubler index; nomenclature; order-disorder; sed rocks, sediments; Sedimentary petrology; sheet silicates; silicates; X-ray data
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1180/0009855023720043

The Nomenclature Committee of AIPEA suggests that the term 'crystallinity index' should not be used, because any deviations from a perfect structure have specific diffraction effects, which may not be measurable by documenting variations of width of a single peak. Instead, it is suggested that the terms 'Hinckley Index', 'Kubler Index' and 'Arkai Index' must be used for kaolinite, illite and chlorite respectively. Due to the existence of a continuum between amorphous and crystalline phases it is necessary to clarify the term 'amorphous', using a description of the diffraction or other properties that suggest the phase is amorphous. The sample preparation techniques and experimental conditions must be reported. Adjectival modifiers may be used to describe amorphous. It is appropriate also to refer to an 'X-ray amorphous' or 'electron amorphous' state if this is determined by XRD or electron diffraction respectively.