Cathodoluminescence of magnesite: Examples from the Eastern Alps

Although cathodoluminescence (CL) microscopy is routinely used in studies of carbonate diagenesis, this technique is rarely applied to the petrographic study of magnesitic rocks. Encouraging results, however, were obtained from very low grade metamorphic magnesite samples from the Eastern Alps. Crystal growth textures, unrecognizable in transmitted light, became clearly visible when a hot-cathode device was used. Spectrophotometric measurements show that Mn 2 + is the only activator, producing a broad emission peak at about 652 nm. Microprobe analyses indicate that the different CL intensities are controlled mainly by varia-tions in the concentrations of Fe 2 +, because Mn 2 + concentrations are consistently high. Quenching of luminescence follows a logarithmic function, and magnesite containing more than 6.5 wt % FeO (corresponding to- 7. 5 mol % FeCC>3) was found to be nonluminescent (i.e., levels of CL were below detection)