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A proposed mechanism for the formation of spherical vivianite crystal aggregates in sediments

Sedimentary Geology

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Abstract

Vivianite [Fe3(PO4)2??8H2O] is often found in the form of nodules composed of spherical aggregates of crystals. Crystallization of vivianite in agar gels of various concentrations yield crystal aggregates (nodules) that have spherical morphology and a bimodal size distribution. The aggregates were formed under both biotic and abiotic conditions. When special redox cells fitted with electrodes were used, more perfect spherical structures were formed when the electrodes were shorted than when they were on open circuit. In nature, vivianite nodules generally are found in sediments or clays that are gelatinous, often caused by the presence of organic debris. A model consistent with experimental observations and based on the dynamics of gels is proposed to explain a possible origin of nodular vivianite. To maintain iron and phosphate concentrations in sedimentary pore spaces filled with gel-like organic debris, the electric field spanning the aerobic-anerobic zones in the upper sediments may be an important driving force in addition to diffusion. It is suggested that the combination of the gel medium in the pore spaces and the natural electric field in the upper sediments could be contributing causes to explain the spherical aggregates of vivianite crystals found in nature. ?? 1988.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A proposed mechanism for the formation of spherical vivianite crystal aggregates in sediments
Series title:
Sedimentary Geology
Volume
59
Issue:
1-2
Year Published:
1988
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
125
Last page:
142
Number of Pages:
18