Calcite, two step activation of Mn via Ce
Contributed by: FMS Admin
Date: Sep 19th, 2025
Locality: Beez quarry, Namur, Namur, Wallonia, Belgium (See on Mindat)
Description:
Calcite skalenohedron, Beez, Namur, Belgium. This a special crystal. Instead of the usual organic yellow fluorescence, it shows an orange Mn2+ fluorescence under 365 nm excitation (black solid line). The orange fluorescence is enhanced via a two step mechanism, in this case Ce3+ (instead of Pb2+). We can see this clearly at 275 nm excitation. The intense purple fluorescence is caused by Ce3+ (black dashed line). It is this Ce that transfers its energy from the excited level to the Mn2+, intensifying that fluorescence. Excitation at 255 nm shows a more yellowish color, caused by the simultaneous presence of multiple bands (grey dotted line).
The crystal is also interesting because it shows a twin line, but it is not a twin. On the visual foto you can see than an oblique angle at the top part has an obtuse counter part in the lower part. This is typical for a single crystal skalenohedron. We assume there is an (invisible) microtwin in the centers that annihilates the twinning effect in the major parts.
Originally posted by groensteenfreterke on Nature’s Rainbow.
Summary of luminescence responses:
Calcite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Orange
- Fluorescence under 275nm LED UV light: Purple
- Fluorescence under Shortwave (255nm LED) UV light: Orange