Some Observations on the Formation, Structure and Morphology of Halloysite
Clay Minerals, (2016) 51, 395–416 Unique but diverse: some observations on the formation, structure and morphology of halloysite G. JOCK CHURCHMAN1,*, P.PASBAKHSH2 ,D.J.LOWE3 AND B.K.G. THENG4 1 School of Agriculture, Food and Wine, University of Adelaide, Adelaide 5005, Australia 2 School of Engineering, Monash University Malaysia, Bandar Sunway, 47500, Selangor, Malaysia 3 School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand 4 Landcare Research, Palmerston North 4442, New Zealand (Received 04 November 2015; revised 11 June 2016; Associate Editor: Steve Hillier) ABSTRACT: New insights from the recent literature are summarized and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ∼8, whereas the tetrahedral sheet is negatively charged at pH > ∼2. The opposing sheet charge would facilitate interlayer uptake of H2O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffraction pattern, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and Fe content may occur within a given sample of halloysite. KEYWORDS: water, pH, iron, particle size, morphology, organic complexes, 2-layer structure. Since halloysite was first described by Berthier (1826), shapes, including spheroidal, platy and prismatic, in the clay mineral has attracted a great deal of attention addition to being fibrous or tubular (Joussein et al., and interest.
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