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Soil Science Society of America Journal Abstract -

Isolation and Characterization of an Iron-rich Chlorite-like Mineral from Soil Clays


This article in SSSAJ

  1. Vol. 54 No. 1, p. 281-287
    Received: Apr 4, 1988

    * Corresponding author(s):
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  1. S. K. Ghabru,
  2. A. R. Mermut  and
  3. R. J. St. Arnaud
  1. Dep. of Soil Science, Univ. of Saskatchewan, Saskatoon, SK, Canada S7N 0W0



This study reports on the isolation and characterization of a naturally occurring Fe-rich, 1.4-nm nonexpanding chlorite-like interphase from soil clays. The mineral was isolated from the coarse clay (2-1 µm) fraction of a Boralf (Gray Luvisol) from Saskatchewan, by using a high-gradient magnetic separation (HGMS) at 0.20-T level of magnetic flux density (MFD). While most chlorites contain Fe2+, analyses showed that all the Fe in this mineral was in the Fe3+ form. High-resolution transmission electron microscopic (HRTEM) examination confirmed a 1.4-nm spacing throughout isolated particles. Iron was extracted from the interlayer of the mineral by repeated dithionite-citrate-bicarbonate (DCB) plus citrate-dithionite (Tamura-CD) extractions. These treatments resulted in the collapse of the mineral from 1.4 nm to 1.0 nm following K-saturation and 105 or 300 °C heating. Extractions of several Fe-rich chlorites with the same DCB and Tamura-CD treatments showed that, although some Fe was extracted from them, they retained their characteristic 1.4-nm spacing after the K-saturation and heat treatments. The DCB and Tamura-CD extractions resulted in a marked increase in cation-exchange capacity (from 27 to 150 cmolc kg−1), and a layer charge of 0.75 per half unit cell. The high initial cation-exchange capacity (CEC) values and the rapid acquisition of a micaceous (1.0-nm) characteristic are atypical of the normal chlorites also included in this study. It is suggested that the mineral isolated is an Fe-hydroxy interlayered vermiculite rather than a true chlorite. Regarding the genesis of the isolated mineral, two possibilities exist: the Fe lost from the octahedral layer of an original mica could have been responsible for the formation of an Fe-hydroxy interlayer, thus producing a chlorite-like mineral, or the interphase may have resulted from weathering of an original chlorite since chlorites were detected in the soil parent material.

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