Iron-Rich High-Charge Beidellite in Vertisols and Mollisols of the High Chaouia Region of Morocco
- Mohammed Badraoui and
- Paul R. Bloom
The mineralogy of Vertisols and Mollisols, associated in a hydrotoposequence in the western part of the phosphate plateau of Morocco (High Chaouia), was studied using x-ray diffraction, interlayer swelling with alkylammonium cations, chemical analysis, and infrared spectroscopy. The swelling behavior of Li- and K-saturated clays demonstrated the beidellitic character of the expandable 2:1 layer silicates that dominate the clay mineralogy of these soils. The beidellite has a heterogeneous layer charge, as measured by the swelling with alkylammonium cations, that ranged from 0.50 to 0.66 charges per half unit cell. The swelling of Li-saturated clays with alkylammonium cations after heating at 300 °C confirmed the tetrahedral location of the charge. Structural formulas calculated for the fine clays showed that the beidellite is similar in all three soils and confirmed that these clays have a high charge density and are Fe rich. Infrared spectroscopy demonstrated that these beidellites contain substantial amounts of Fe3+ in the octahedral sheet. Kaolinite, chlorite, palygorskite, and quartz were also present, especially in the coarse-clay fractions and in the subsoil. The presence of this Fe-rich, high-charge beidellite in the soils helps explain the behavior of soil K and also offers an explanation of K soil test interpretation problems.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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