Calcium Carbonate Concretions Formed by the Decomposition of Organic Matter

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Science  12 Jan 1968:
Vol. 159, Issue 3811, pp. 195-197
DOI: 10.1126/science.159.3811.195


Bacterial decomposition of butterfish and smelts in small sealed jars containing seawater and other solutions, for periods ranging from 65 to 205 days, results in a large increase in concentrations of dissolved bicarbonate, carbonate, and ammonia (plus volatile amines). Accompanying this is a rise in pH and the precipitation of Ca++ ion from solution. The Ca++ is not precipitated as CaCO3 but instead as a mixture of calcium fatty acid salts or soaps with from 14 to 18 carbon atoms. This can be explained by the thermodynamic instability of CaCO3 relative to Ca soaps in the presence of excess free fatty acid. It is suggested that some ancient CaCO3 concretions, especially those enclosing fossils of soft-bodied organisms, may have formed rapidly after death in the form of natural Ca soap (adipocere) which was later converted to CaCO3.

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