Mineralogical and geochemical aspects of geophagic clayey soils from the Democratic Republic of Congo

Abstract

Clayey soil samples ingested by the people of the Democratic Republic of Congo (DRC) were obtained in their physical state of ingestion, from selected localities in the country. The particle size, minerals contents and geochemical composition of the samples were determined in order to establish baseline information on mineralogy and geochemistry of geophagic soils in DRC. The geophagic clayey soils were whitish, light grayish to brownish in colour and their textures were silt, silt loam, silty clay loam and silty clay. From X-ray diffractometry analysis, the following twelve minerals were identified in the samples: quartz and kaolinite being the most dominant, followed by muscovite, and others in minor to trace being talc, microcline, goethite, haematite, siderite, gibbsite, anatase, smectite and halite which is added in processed samples for taste. Concentrations of SiO2 and Al2O3supported identified kaolinite abundance in the samples. Kaolinite, which is the main desirable mineral component of the geophagic clayey soils, was geochemically derived from surrounding granites, rhyolites and basalts. Derivation of secondary minerals contained in the geophagic clayey soils were further substantiated from values obtained for chemical index of alteration (CIA) (80.25 to 99.68) and chemical index of weathering (CIW) (95.59 to 99.94) which were supportive of intense weathering environment for the formation of the clayey soils. Key words: Chemical index of alteration, geophagia, kaolinite, quartz, soil texture.