Mineral phases and processes within green peloids from two Recent deposits near the Congo River Mouth

P. Giresse, A. Wiewiora, B. Lacka
1988 Clay minerals  
In the Recent sediments of the Congo River estuary, the green Fe-bearing peloids containing 7 Å phases are nearer to the river mouth than the 10 Å phyllosilicates. Measurements of d 060 for 7 Å minerals in various density fractions indicated a progressive transformation of kaolinite into trioctahedral 1:1 phyllosilicates in the zone with a high sedimentation rate. Projection of the chemical composition from the approximate crystallochemical formula on to a classification field confirmed the
more » ... sformation of kaolinite into a 7 Å Fe-rich phase via substitution of Fe2+ and Mg for Al in the octahedral sheet, with insignificant changes in the tetrahedral sheet. The resultant transition phase has a composition closer to greenalite than berthierine. The possible advancement of the evolution process was stopped by massive formation of goethite. The 10 Å minerals formed in the grains deposited in the off-shore sediments have a homogenous composition and occur in association with goethite and quartz. These peloids show an enrichment in Al although no kaolinite is present.
doi:10.1180/claymin.1988.023.4.11 fatcat:6274n57ourd63i2qmurrpnejza