Identification of calcite grains in the Vaca Muerta mesosiderite by Raman spectroscopy

Within the framework of a detailed micro-Raman study of Vaca Muerta mesosiderite, the Raman spectra of calcite globules inside the meteorite are reported for the first time. These spectra were compared with spectra of terrestrial calcite of sedimentary, hydrothermal and magmatic origin under the same experimental conditions. Some differences are found in the relative intensities and bandwidths between Vaca Muerta and terrestrial calcite spectra, which cannot be assigned to micro-crystal orientations effects. The origin of these calcite globules is discussed. Although a secondary mineral process due to terrestrial weathering after the fall can not be completely discarded, two hypotheses are proposed. The first addresses the possibility of the formation of calcite with small structural changes due to shocks at various times in the complex history of the meteorite. The second is related to the very recent discovery of carbonates (calcite and dolomite), not formed by aqueous alteration, in the dust shells of evolved stars. Copyright (C) 2003 John Wiley Sons, Ltd.