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The nature of smectites and associated interstratified minerals in soils of the Gharb plain of Morocco

1996; Wiley; Volume: 47; Issue: 2 Linguagem: Inglês

10.1111/j.1365-2389.1996.tb01387.x

1365-2389

Rachid Bouabid, Mohammed Badraoui, Paul R. Bloom, M. DANIANE,

Geological and Geophysical Studies Worldwide

Summary The mineralogies of ‘Tirs’ (Typic Pelloxererts), and ‘Debs’ (Typic Haploxerolls and Typic Xerochrepts) soils of the Gharb plain in north‐western Morocco are investigated, with special attention given to the determination of the nature of the smectitic phase using the lithium test (Li test) and the alkylammonium method. The sand and silt mineralogy of Tirs soils is dominated by quartz with small amounts of feldspars and kaolinite. The sand and silt fractions of Dehs soils also contain significant amounts of mica, chlorite, and interstratified phyllosilicates. The clay minerals of Tirs soils are predominantly a high‐charge smectite. The estimated interlayer charge for this phase is 0.61 mol(c)/O 10 (OH) 2 and the fraction of tetrahedral charge varies from 38 to 44%. Although the percentage tetrahedral charge is less than 50%, the smectitic phase behaves as beidellite with the Li test. Dehs clays are more heterogeneous, consisting of smectite, vermiculite, illite, kaolinite, chlorite, and interstratified illite/smectite and illite/vermiculite. The Li test and the alkylammonium method demonstrate that a high‐charge smectite or vermiculite is interstratified with illite. A low‐charge montmorillonite is also present both in Tirs and in Dehs soils. The high‐charge beidellitic phase is believed to be a transformation product of mica, whilst the low charge montmorillonite is thought to be inherited from the parent material.