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Iron‐Rich High‐Charge Beidellite in Vertisols and Mollisols of the High Chaouia Region of Morocco
Author(s) -
Badraoui Mohammed,
Bloom Paul R.
Publication year - 1990
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1990.03615995005400010043x
Subject(s) - vertisol , chlorite , clay minerals , kaolinite , subsoil , soil water , quartz , mineralogy , infrared spectroscopy , charge density , materials science , geology , chemistry , soil science , composite material , organic chemistry , physics , quantum mechanics
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 Fe 3+ 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.