Clays and Clay Minerals, Vol. 58, No. 2, 238–246, 2010.
Loading...
Authors
Nieto, Fernando
Mellini, Marcello
Abad, Isabel
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Composition , Hydronium , Illite , Water
Alternative Title
The Role Of H3O+ In The Crystal Structure Of Illite
Abstract
In spite of decades of research on the subject, the crystal structure of illite is still poorly understood. The purpose of this study was to address this problem by investigating the nature of the interlayer content in illite IMt-2 from Silver Hill, Montana, using analytical transmission electron microscopy (ATEM), thermogravimetry (TG), and X-ray powder diffraction (XRPD) analyses. The ATEM data, together with literature andTG results, yieldedthe formula K0.70Na0.01(H2O)0.42 (Al1.53Fe2+ 0.06Fe3+ 0.19Mg0.28)S=2.06(Si3.44Al0.56)O10(OH)2 or, assuming the presence of H3O+, K0.69Na0.01(H3O)+ 0.28(Al1.47Fe2+ 0.06Fe3+ 0.19Mg0.28)S=1.99(Si3.40Al0.60)O10(OH)2. The first formula indicates surplus interlayer andoctahed ral species, whereas the secondshows no excess. The XRPD data were refinedby Rietveldte chniques, down to an Rp factor of 10.48-13.8%. The mineral composition consists largely of illite-2M1, illite-1M, andminor quartz. Although the refinement accuracy is limitedby the intrinsic poor quality diffraction of the illites, the partially refined model is consistent with the chemical composition; in particular, attempts to introduce octahedral cations in excess of 2 were fruitless. All the results support the simple structural model, by which the illite structure strictly corresponds to a dioctahedral mica with H3O+ replacing K. As a consequence, the crystalchemical formula of illites should be calculated on the basis of six tetrahedral plus octahedral cations.
Description
gsccm58208-nie.pdf -- 380KB
Citation
Clays and Clay Minerals, Vol. 58, No. 2, 238–246, 2010.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018