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Crystal structure and growth fabric of length-fast chalcedony

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Abstract

Chalcedony from Brazilian agates, has been investigated by using transmission-electron microscopy, X-ray-diffraction, thermogravimetry and optical techniques.

The quartz fibers of length-fast chalcedony are composed of submicroscopical polysynthetic, lamellar-twinned right- and lefthanded crystals, according to the Brazil law. This very narrow twinning causes 3 systems of diffuse diffraction streaks (corresponding to the three-fold symmetry) parallel to 〈10.1〉, very frequently possessing an intensity maximum at h±1/2, k, l±1/2. These extra reflections were detected both in electron- and X-ray-diffraction patterns.

Wall-lining chalcedony is parallel fibrous consisting of smaller crystallites with a higher total water content (0.06±0.01 μm and 1.2±0.1 wt %) than spherulitic chalcedony in horizontal agate bands (ca. 0.1 μm and 0.7±0.1 wt%).

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Authors and Affiliations

  1. Institut für Kristallographie der Universität Frankfurt, Senckenberg-Anlage 30, 6000, Frankfurt, West Germany

    G. Miehe

  2. Institut für Mineralogie der Ruhr-Universität Bochum, Universitätsstr. 150, 4630, Bochum, West Germany

    H. Graetsch & O. W. Flörke

Authors
  1. G. Miehe
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  2. H. Graetsch
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  3. O. W. Flörke
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Miehe, G., Graetsch, H. & Flörke, O.W. Crystal structure and growth fabric of length-fast chalcedony. Phys Chem Minerals 10, 197–199 (1984). https://doi.org/10.1007/BF00309311

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  • DOI: https://doi.org/10.1007/BF00309311

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