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The role of minor element substitutions on marine mineral solubilities and formation and dissolution kinetics
Applied Geochemistry, Vol. 3, p. 114, 1988
0883-2927/88 $3.(X) + .00 Pergamon Press plc
Printed in Great Britain
The role of minor element substitutions on marine mineral solubilities and formation and dissolution kinetics RICHARD JAHNKE Scripps Institution of Oceanography, La Jolla, CA 92093, U.S.A.
REACTIONS occurring in marine sediments play a crucial role in the marine geochemical cycles of many important elements. These reactions include both the removal of solutes into authigenic mineral phases as well as the release of dissolved species by the dissolution of thermodynamically unstable phases. One would like to establish an approximate thermodynamic and/or kinetic framework in which to describe and predict the sequence of mineral assemblages retained in the geological record. However, several factors limit the application of thermodynamic or kinetic models to this complex system. The existing thermodynamic and kinetic data has, in general, been determined for pure mineral phases, whereas most minerals in marine sediments exhibit a variety of isomorphic substitutions. The influence of these substituting ions on mineral solubility and for-
mation or dissolution kinetics is, for the most part, unknown. Also, the role of organisms in mediating the formation and determining the composition of authigenic mineral phases is not understood. Clearly, a complete thermodynamic and kinetic description of this system is not a realistic short-term goal. However, quantitative models, which could be developed to describe specific individual minerals or groups of minerals, would be a large step forward. Studies of selected minerals would be greatly aided by improved methods by which marine minerals could be synthesized and examined in the laboratory under realistic aqueous conditions. Additionally, surface analysis techniques, which may be applied to small mineral grains, (<10 /~m) would greatly increase our ability to study substitutions in natural and synthetic mineral phases on realistic time-scales.
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0883-2927/88 $3.(X) + .00 Pergamon Press plc
Printed in Great Britain
The role of minor element substitutions on marine mineral solubilities and formation and dissolution kinetics RICHARD JAHNKE Scripps Institution of Oceanography, La Jolla, CA 92093, U.S.A.
REACTIONS occurring in marine sediments play a crucial role in the marine geochemical cycles of many important elements. These reactions include both the removal of solutes into authigenic mineral phases as well as the release of dissolved species by the dissolution of thermodynamically unstable phases. One would like to establish an approximate thermodynamic and/or kinetic framework in which to describe and predict the sequence of mineral assemblages retained in the geological record. However, several factors limit the application of thermodynamic or kinetic models to this complex system. The existing thermodynamic and kinetic data has, in general, been determined for pure mineral phases, whereas most minerals in marine sediments exhibit a variety of isomorphic substitutions. The influence of these substituting ions on mineral solubility and for-
mation or dissolution kinetics is, for the most part, unknown. Also, the role of organisms in mediating the formation and determining the composition of authigenic mineral phases is not understood. Clearly, a complete thermodynamic and kinetic description of this system is not a realistic short-term goal. However, quantitative models, which could be developed to describe specific individual minerals or groups of minerals, would be a large step forward. Studies of selected minerals would be greatly aided by improved methods by which marine minerals could be synthesized and examined in the laboratory under realistic aqueous conditions. Additionally, surface analysis techniques, which may be applied to small mineral grains, (<10 /~m) would greatly increase our ability to study substitutions in natural and synthetic mineral phases on realistic time-scales.
114