The spectral composition of the visible thermoluminescence (TL) glow emitted by various natural crystals of sphene and epidote has been studied. All naturally damaged samples (the amount of damage being monitored by their fossil fission track density) were found to exhibit a reduced contribution in the spectral component lying in the blue-green region (∼ 400–500 nm) relative to that from undamaged ones. It was found that, in the case of sphene, the ratio ( R) of emission at shorter wavelengths (typified by 455 nm) to that at longer wavelengths (represented by 570 nm) decreases with the increase of fission track density, indicating a shift of spectral emission towards the red region (> 600 nm). For epidote a strong anticorrelation was observed between natural damage and the ratio ( S) of emission spectral intensity at 400–500 nm to the total glow in the region of 400–600 nm. Furthermore, when the degree of damage in both minerals was varied by means of annealing the samples (for 1 h) at various temperatures from 100°C upwards, the ratio R of emission at 455 nm to that at 570 nm, in response to a test dose of γ-rays, was found, in the case of sphene, to increase linearly with the increase of annealing temperature; i.e. as the damage was healed, the TL emission shifted towards the blue. For epidote samples, on the other hand, the ratio S was found to increase with the increase of annealing temperature up to 700°C, and then to fall again at higher temperatures of annealing. For comparison, the effect of artificially induced damage on the TL spectrum of sphene was also investigated. This was done by bombarding undamaged sphene with ∼ 30 Mev 4He particles from a cyclotron at fluences of 10 12–10 16 α cm −2. Again, the relative emission (455 nm: 570 nm) was found to decrease with increasing magnitude of α-fluence, i.e. with increasing damage. Finally, an X-ray diffraction study of naturally damaged sphene showed an increase in the unit cell dimensions of the crystal with increasing damage (i.e. increase of fossil fission track density). When damaged samples were annealed at various temperatures (200–1000°C) for 1 h, a significant decrease in cell dimensions at annealing temperatures between 200 and 600°C was observed, though the change was quite small beyond the annealing temperature of 600°C. The above pattern of change in the rate of decrease in cell dimensions indicates that the annealing of radiation damage in sphene is a multistage process. This observation is in line with the two-phase change in the TL sensitivity reported by Khalifa and Durrani (1986) and by Durrani and Khalifa (1988). In the case of epidote, the most significant change in the crystal structure as a function of annealing temperature appears to occur in the angle β and the unit cell dimension a.