The effect of annealing temperature on the structural, thermoluminescence, and optical properties of the thermally treated naturally occurring salt from Lluta were studied. Samples were submitted to different annealing temperatures from 300 to 700 °C for 30 min. X-ray diffraction analysis of all samples was performed. The predominant crystalline phase found in the Lluta salt sample is NaCl, with minor phases (CaSO4 and Na). TL technique has been used to characterize and determine the dosimetric properties. After the thermal annealing process of samples, an increase in the TL response of up to 80 times the TL intensity of the natural sample is observed. A promising dosimetric high-temperature peak was found for the sample with an annealing temperature of 400 °C for 30 min. Besides, activation energy, frequency factor, and peak position have been determined by E-Tstop, Tm-Tstop, and deconvolution methods. The UV–Vis optical absorption of Lluta salt sample subjected to several annealing temperatures was investigated. The optical energy gap Eg was calculated using the Tauc relation and the relation between the variation of the optical band gap and the density of thermoluminescent traps was analyzed.