Mathematics – Logic
Scientific paper
Oct 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986gecoa..50.2195p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 50, Issue 10, pp.2195-2203
Mathematics
Logic
22
Scientific paper
The incorporation of Sr 2+ into calcite at earth surface aqueous conditions is affected by the absolute concentration of Sr 2+ , the presence of Ba 2+ and NaCl in the solution, and the rate of precipitation. At solution ratios (molar) of Sr 2+ to Ca 2+ in the low 10 -3 range, which yield calcites with several hundred ppm Sr 2+ , K sr calcite typically assumes a value between 0.10 and 0.20. Above these concentrations the value of k Sr calcite drops to approximately 0.06. Furthermore, if minor amounts of Ba 2+ or large amounts of Na + (0.48 M) are added to a dilute Sr 2+ solution, a value around 0.06 for k Sr calcite is found. This "strontium concentration effect" and the associated "competitive cation effect" suggest that small amounts of Sr 2+ may be incorporated into a limited number of nonlattice sites in calcite. Incorporation of Sr 2+ into these sites, presumably defects, noticeably affects k Sr calcite only at low Sr 2+ concentrations and in the absence of competition from other large cations. An increase in k Sr calcite with rate of precipitation, qualitatively similar to that found in other studies, was observed only when precipitation times were decreased from days to hours. For many geologic settings a partition coefficient for Sr 2+ into calcite of 0.06 appears appropriate, but there are situations--very low Sr 2+ concentrations, the presence of Mg 2+ , and fast precipitation rates--in which a larger value might better approximate natural partitioning.
Eastman Michael P.
Pingitore Nicholas E. Jr.
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