[en] We report a spurious thermoluminescence (TL) present in three types of calcite powders which also show regenerated TL (RTL). The amount of RTL was found on storage time and on the heating rate used during TL readout. Different heating rates during TL readout caused profound changes in the measured TL spectra in the range 400-650 nm. These changes can be explained by manganese ions moving into and out of clusters during the heating process. (author)