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Crystal Structure Refinement and Mössbauer Spectroscopy of an Ordered, Triclinic Clinochlore

Published online by Cambridge University Press:  28 February 2024

Joseph R. Smyth
Affiliation:
Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250
M. Darby Dyar
Affiliation:
Department of Geology and Astronomy, West Chester University, West Chester, Pennsylvania 19383
Howard M. May
Affiliation:
US Geological Survey, Water Resources Division, 3215 Marine Street, Boulder, Colorado 80303
Owen P. Bricker
Affiliation:
US Geological Survey, Reston, Virginia 22092
James G. Acker
Affiliation:
US Geological Survey, Reston, Virginia 22092

Abstract

The crystal structure of a natural, ordered IIb-4 triclinic clinochlore has been refined in space group C1̄ from 4282 unique X-ray intensity measurements of which 3833 are greater than 3 times the statistical counting error (3σ). Unit cell parameters are a = 5.3262(6) Å; b = 9.226(1) Å; c = 14.334(3) Å; α = 90.56(2)°; β = 97.47(2)°; and γ = 89.979(9)°, which represents the greatest deviation from mono-clinic symmetry yet recorded for a triclinic chlorite. The final weighted R is 0.059 for reflections with I > 3σ and 0.064 for all reflections. The chemical formula is (Mg0.966Fe0.034)MI(Mg0.962Fe0.038)M22(Si2.96Al1.04)O10 (OH)2(Mg0.996Fe0.004)M32(Al0.841FeIII0.102Cr0.004Ti0.004)M4(OH)6, which is consistent with electron microprobe (EMP), wet chemical analyses, Mössbauer spectroscopy and X-ray structure refinement. The high degree of ordering of the divalent versus trivalent octahedral cations in the interlayer is noteworthy, with FeIII and Al in M4 and virtually no Fe in M3. In the 2:1 layer, M1 and M2 each contain similar amounts of Fe. The 2 tetrahedral sites have nearly identical mean oxygen distances and volumes, and thus show no evidence of long-range cation ordering.

Information

Type
Research Article
Copyright
Copyright © 1997, The Clay Minerals Society

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