Radiaxial Fibrous Calcite: A Replacement after Acicular Carbonate

  1. Maurice E. Tucker2 and
  2. Robin G. C. Bathurst3
  1. A. C. Kendall and
  2. M. E. Tucker

Published Online: 29 APR 2009

DOI: 10.1002/9781444304510.ch14

Carbonate Diagenesis

Carbonate Diagenesis

How to Cite

Kendall, A. C. and Tucker, M. E. (1990) Radiaxial Fibrous Calcite: A Replacement after Acicular Carbonate, in Carbonate Diagenesis (eds M. E. Tucker and R. G. C. Bathurst), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304510.ch14

Editor Information

  1. 2

    Department of Geological Sciences, University of Durham, UK

  2. 3

    Derwen Deg Fawr, Llanfair DC, Ruthin, Clwyd, North Wales, UK

Author Information

  1. Department of Geological Sciences, University of Durham, UK

  1. School of Earth Sciences, University of East Anglia, Norwich, UK

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 21 AUG 1990

ISBN Information

Print ISBN: 9780632029389

Online ISBN: 9781444304510

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Keywords:

  • radiaxial fibrous calcite - a replacement after acicular carbonate;
  • curved twin lamellae, characterizing radiaxial fibrous calcite;
  • crystals, being turbid with inclusions;
  • fibrous calcite intercrystalline boundaries, forming fractures after replacement;
  • replacement, taking place by solution-precipitation process

Summary

Radiaxial fibrous calcite, a common cavity fill in ancient limestones, is characterized by curved twin lamellae, optic axes that converge away from the substrate and subcrystals which diverge in this same direction. The optic axes radiate about three or four axes located in positions between adjacent crystals and orientated parallel with the crystal elongation. The crystals are commonly turbid with inclusions, which may be concentrated along twin lamellae and subcrystal and intercrystalline boundaries, or form zones parallel to the substrate. Some inclusion patterns reveal the position of former crystal faces.

From a consideration of the occurrences, gross morphological characters, the fabrics of the crystals and the inclusion patterns, radiaxial fibrous calcite is interpreted as a replacement of an early diagenetic acicular cement, composed of interfering bundles of radiating crystals. It is suggested that replacement takes place by a solution-precipitation process and the migration of a fluid film through the acicular host, with replacement occurring most rapidly between bundles of acicular carbonate. The optic axis pattern of the fibrous calcite is considered to be inherited from the c-axis orientations of the host acicular crystals. Fibrous calcite intercrystalline boundaries form as fractures after replacement. Some inclusion patterns record the characters of the replaced acicular cement; others, formed of impurities reorganized during the replacement, reveal the form of the replacement front.