Mathematics – Logic
Scientific paper
Apr 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.1531p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 56, Issue 4, pp.1531-1538
Mathematics
Logic
7
Scientific paper
By probing the local atomic environment of strontium coprecipitated with natural and synthetic calcites, X-ray absorption spectroscopy (XAS) reveals that the strontium is incorporated in the calcite by substitution at Ca 2+ structural sites, forming a dilute solid solution. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) demonstrated that the local structural environment of Sr 2+ in natural and synthetic calcites was similar to that of Ca 2+ in calcite and quite different from that of Sr 2+ in strontianite. The Sr 2+ -O 2- distance derived from EXAFS, 2.58 ± 0.03Å, is consistent with the sum of the radii of these two ions in six- and three-fold coordination, respectively, of 2.57 Å. The XANES and EXAFS further eliminate such modes of incorporation as adsorption, occlusion, and the presence of trace amounts of strontianite or other Sr 2+ -rich phase. However, evidence of a possible relict Sr 2+ -rich aragonite was encountered in a diagenetic calcite, indicating that XAS may prove a sensitive tool for detecting incomplete mineralogical alteration in carbonates. Because Sr 2+ is bound at Ca 2+ lattice sites, the record of biomineralization, diagenesis and age encoded in Sr 2+ / Ca 2+ ratios, and strontium isotopes in geologic calcites is secure; likewise, 90 Sr sequestered in natural calcite should not undergo significant preferential leaching.
Davies Brian M.
Eastman Michael P.
Eller Gary P.
Larson Elizabeth M.
Lytle Farrel W.
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