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Mechanism and Controls of Silicification of Fossils in Limestones

Robert G. Maliva and Raymond Siever
The Journal of Geology
Vol. 96, No. 4 (Jul., 1988), pp. 387-398
Stable URL: http://www.jstor.org/stable/30062155
Page Count: 12
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Mechanism and Controls of Silicification of Fossils in Limestones
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Abstract

Silicification of calcitic fossils occurs along thin solution films at which calcite dissolves and silica precipitates. The mechanism is replacement controlled by force of crystallization, whereby the growth of the silica phase exerts pressure across the silica-carbonate contact, increasing the Gibbs free energy and hence solubility of shell calcite. Physical evidence for force of crystallization-controlled replacement includes restriction of carbonate dissolution to the silica-carbonate contact, and euhedral quartz terminations at some quartz-calcite contacts. Correlations among some replacement quartz types and fossil taxa indicate that shell microstructure and bulk pore water silica concentration control replacement quartz type.

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