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    The replacement of a carbonate rock by fluorite: Kinetics and microstructure

    Access Status
    Fulltext not available
    Authors
    Pedrosa, E.
    Boeck, L.
    Putnis, C.
    Putnis, Andrew
    Date
    2017
    Type
    Journal Article
    
    Metadata
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    Citation
    Pedrosa, E. and Boeck, L. and Putnis, C. and Putnis, A. 2017. The replacement of a carbonate rock by fluorite: Kinetics and microstructure. American Mineralogist. 102 (1): pp. 126-134.
    Source Title
    American Mineralogist
    DOI
    10.2138/am-2017-5725
    ISSN
    0003-004X
    School
    The Institute for Geoscience Research (TIGeR)
    URI
    http://hdl.handle.net/20.500.11937/51119
    Collection
    • Curtin Research Publications
    Abstract

    © 2017 by Walter de Gruyter Berlin/Boston.Understanding the mechanism and kinetics of the replacement of carbonates by fluorite has applications in Earth sciences and engineering. Samples of Carrara marble were reacted with an ammonium fluoride (NH4F) solution for different reaction times and temperatures. The microstructure of the product phase (fluorite) was analyzed using SEM. The kinetics of replacement was monitored using Rietveld refinements of X-ray powder diffraction patterns of the products. After reaction, all samples preserved their size and external morphology (a pseudomorphic replacement). The grain boundaries of the original marble were preserved although each calcite grain was replaced by multiple fine crystals of fluorite creating inter-crystal porosity. The empirical activation energy Ea (kJ/mol) of the replacement reaction was determined by both model-fitting and model-free methods. The isoconversional method yielded an empirical activation energy of 41 kJ/mol, and a statistical approach applied to the model-fitting method revealed that the replacement of Carrara marble by fluorite is better fitted to a diffusion-controlled process. These results suggest that the replacement reaction depends on the ion diffusion rate in the fluid phase through the newly formed porosity.

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