Room-temperature dehydration of aqueous coal slurries, coal extraction residue, or coal ash results in spontaneous luminescence. The phenomenon is characterized by a monotonic decay in photon activity which precedes a sharp rise in photon release. A maximum is reached within several minutes but subsequent decay is slower and photon emission continues for an extended period of time. The magnitude of photon activity is severely limited by the thickness of the strongly absorbing coal slurry. Prior removal of mineral matter from the coal appears to curtail the dehydration-induced phenomena, suggesting that clays or clay-organic interactions are responsible. Data also suggest that air is required as a medium for discharging the excited species.