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Infrared Spectra and Elemental Composition in Recent Biogenic Calcites: Relationships between the upsilon 4 Band Wavelength and Sr and Mg Concentrations

Volume 53, Number 2 (Feb. 1999) Page 184-190

Dauphin, Y.


Biogenic calcites show various chemical contents (Sr and Mg) related to the systematic position of the organisms. It is well known that algae, octocorallia, and echinoderm tests are composed of high Mg calcites, whereas mollusc shells are composed of lower Mg calcites. DRIFT (diffuse reflectance infrared Fourier transform) spectra show that the frequency of the upsilon 4 band significantly differs in the high Mg calcite and low-Mg calcite set. The upsilon 1 band and the doublet upsilon 2 do not seem to be altered. There is a strong positive linear correlation between the upsilon 4 wavelength and Mg concentrations in these biological calcites. The linear correlation between the upsilon 4 wave- length and Sr concentrations is only 0.59. It is known that the calcite-dolomite transition shifts the wavelength of the upsilon 4 band, but such a shift has not been observed in the single calcite.