Raman spectroscopic characterization of the magnesium content in amorphous calcium carbonates

A series of Mg‐bearing synthetic amorphous calcium carbonates (ACC) were characterized by Raman spectroscopy. The spectra showed a systematic increase in the carbonate ν 1 peak position from the control samples that contained 0.0 mol % MgCO 3 to samples that contained up to 43 mol % MgCO 3 . The relationship is best described by the function: mol % MgCO 3 = (ν 1 – 1079.66) / 0.2017. The Mg content is equally well‐predicted by a correlation with the instrumentally corrected ν 1 full width at half maximum that is quantified by: mol % MgCO 3 = (ν 1 – 23.26) / 0.1969. An analysis of the Raman data collected for ACC combined with insights from crystalline materials suggests that compositional dependencies arise from changes in the local metal–oxygen bonds as Mg substitutes for Ca. The calibrations described here provide a rapid and nondestructive means of determining the Mg content of ACC, with additional advantages of minimal sample preparation and a high degree of lateral spatial resolution (approximately 1 µm). This method may be appropriate for investigations of heterogeneous samples such as biominerals. Copyright © 2011 John Wiley & Sons, Ltd.