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Formation of vivianite in holocene clay sediments |
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| Authors: | I Th Rosenqvist |
| Institution: | Rosenqvist, Institute of Geology, University of Oslo, Blindern, Oslo3, Norway |
| Abstract: | Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay. Solubility product of vivianite is determined. The equilibrium constant is K = 10?40 for the reaction 3 Fe++ + 2 HPO4? + 2 OH? = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed. |
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