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The Crystal Structure of Stilpnomelane Part I. The Subcell

Published online by Cambridge University Press:  01 January 2024

R. A. Eggleton  and
S. W. Bailey
R. A. Eggleton
Affiliation:
University of Wisconsin, Madison, Wisconsin, USA
S. W. Bailey
Affiliation:
University of Wisconsin, Madison, Wisconsin, USA
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Abstract

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Ferric-iron stilpnomelane is triclinic, space group Pl, a = 21.724 Å, b = 21.724 Å, c = 17.740 Å, α = 124.14°, β = 95.86°, γ = 120,0°, Z = 16. The structure is dominated by a subcell for which as = 1/4a, bs = 1/4b, cs = 1/4c, αs = α, βs = β, γs = γ. The subcell reflections have h-k = 3n, and have a trigonal intensity distribution. The structure was determined from Patterson projections and by trial and error. Three-dimensional refinement by least squares gave an it! factor of 14.4 per cent for 296 reflections.

Stilpnomelane is a layer structure, having five anion and five cation planes parallel to (001). An iron-rich octahedral sheet is flanked by two tetrahedral sheets. The tetra-hedral sheets differ from those found in the common layer silicates in that adjacent tetrahedra point in opposite directions. Each tetrahedral sheet has 1.25 tetrahedra pointing toward the octahedral sheet, and 0.75 tetrahedra pointing away. Detail in the tetrahedral sheet cannot be determined from the subcell reflections only.

Type
Symposium on Structural Aspects of Layer Silicate
Information
Clays and Clay Minerals (National Conference on Clays and Clay Minerals) , Volume 13 , February 1964 , pp. 49 - 63
Copyright
Copyright © The Clay Minerals Society 1964

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