We report a spurious thermoluminescence (TL) present in three types of
calcite powders which also show regenerated TL (RTL). The amount of R
TL was found to depend on storage time and on the heating rate used du
ring TL readout. Different heating rates during TL readout caused prof
ound 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 clu
sters during the heating process. (C) 1997 Elsevier Science Ltd.