The illite-aluminoceladonite series; distinguishing features and identification criteria from X-ray diffraction and infrared spectroscopy data

Al-rich K-dioctahedral 1M and 1Md micas are abundant in sedimentary rocks and form a continuous compositional series from (Mg,Fe)-poor illite to aluminoceladonite through Mg-rich illite. The complexity and heterogeneity of chemical composition and structural features, as well as the lack of reliable...

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Bibliographic Details
Published in:Clays and clay minerals 2015-10, Vol.63 (5), p.378-394
Main Authors: Zviagina, Bella B, Drits, Victor A, Srodon, Jan, McCarty, Douglas K, Dorzhieva, Olga V
Format: Article
Language:English
Subjects:
Aluminoceladonite
aluminosilicates
Biogeosciences
celadonite
chemical properties
clay mineralogy
Dioctahedral Mica
Earth and Environmental Science
Earth Sciences
experimental studies
FTIR spectra
FTIR SPECTROSCOPY
Geochemistry
identification
Illite
infrared spectra
Medicinal Chemistry
mica group
Mineralogy
Nanoscale Science and Technology
sed rocks, sediments
Sedimentary petrology
sheet silicates
silicates
Soil Science & Conservation
spectra
Unit-Cell Parameters
X-Ray Diffraction
X-ray diffraction data
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Summary:Al-rich K-dioctahedral 1M and 1Md micas are abundant in sedimentary rocks and form a continuous compositional series from (Mg,Fe)-poor illite to aluminoceladonite through Mg-rich illite. The complexity and heterogeneity of chemical composition and structural features, as well as the lack of reliable diagnostic criteria, complicate the identification of these mica varieties. The objectives of the present study were to reveal the structural and crystal-chemical variability in the illite-aluminoceladonite series, and to define the composition ranges and identification criteria for the mica varieties in the series. A collection of illite and aluminoceladonite samples of various compositions was studied by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. Analysis of the relationships between unit-cell parameters and cation composition showed that the series includes three groups, (Mg,Fe)-poor illites, Mg-rich illites, and aluminoceladonites, each characterized by a unique combination of unit-cell parameter variation ranges. The distinctive features of aluminoceladonite are reduced values of csinβ and |ccosβ/a| in combination with b parameters that are smaller than those for Mg-rich illites, and slightly greater than those of (Mg,Fe)-poor illites. The compositional boundary between illite and aluminoceladonite occurs at Si=∼3.7 and Mg+Fe2+=∼0.6 atoms per O10(OH)2. A new approach to the interpretation of the FTIR spectroscopy data involving new relationships between band positons and cation composition of (Mg,Fe)-poor illites, Mg-rich illites, and aluminoceladonites provides additional diagnostic features that include the band positions and profile in the regions of Si-O bending, Si-O stretching, and OH-stretching vibrations. A sharp maximum from the AlOHMg stretching vibration at ∼3600 cm-1, the presence of a MgOHMg stretching vibration at 3583-3585 cm-1, as well as characteristic band positions in the Si-O bending (435-439, 468-472, and 509-520 cm-1) and stretching regions (985-1012 and 1090-1112 cm-1), are typical of aluminoceladonite.
ISSN:0009-8604
1552-8367
DOI:10.1346/CCMN.2015.0630504