Influence of the Mg-content on ESR- Signals in Synthetic Calcium Carbonate

Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal attice from calcite to aragonite. The properties of the ESR-signals of the synthetic arbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg2+-ions the synthetic arbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g = 2.0006 in synthetic alcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g = 2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Itssaturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g = 2.0031 appeared. (d) The signals at g = 2.0057 and g = 2.0031 are most probably not of organic origin. 1