Cathodoluminescence of calcite decomposed from dolomite in high–temperature skarn

Abstract

Purple-cathodoluminescent calcite associated with periclase and survival dolomite has been found from the skarn minerals in the Kanehira mine located in the eastern part of Hiroshima Prefecture. Paragenesis of these minerals suggests that the decomposition of dolomite at 700-750°C under dry condition during skarnitization could promote the production of characteristic calcite. Cathodoluminescence (CL) spectroscopy of the calcite reveals its blue emissions related to defect centers possibly derived from its origin, also similar CL features in the dolomite. Spectral deconvolution of the CL in the calcite and dolomite clarified two emission components at 2.67 and 3.30 eV, of which former corresponds to structural defect by thermally-influenced stress and the latter to intrinsic defect comparable to 'back ground blue' previously reported in calcite. The facts imply that the calcite with purple CL might leave the defects in its structure during thermal decomposition of dolomite at relatively high-temperature skarnization.

Luminescence reveals variations in local structural order of calcium carbonate polymorphs formed by different mechanisms

“…A process similar to plaster production has been observed by Kusano et al . 39 in geogenic skarn formations, where limestone and dolomite are altered to CaO by contact with hydrothermal fluids and show strong blue emissions together with minor orange ones. Shell C1 and C2, which were heated to relatively low temperature, also show strong blue emissions (Fig.…”