The kinetics and chemical reaction mechanisms involved in the decomposition of eggshells are studied by experimental (thermogravimetric analysis and differential thermal analysis) as well as theoretical models. X-ray diffraction pattern of calcined eggshell at 1000 °C for 4 h exhibits monophasic CaO. The optical band gap of eggshell powder is observed 4.06 eV, which is less than commercial CaCO 3 (4.32 eV). The results showed that the activation energy for decomposition calculated through different methods is in good agreement with the reported value, i.e., in the range of 207–214 kJ mol −1 . Based on Raman spectroscopy, eggshells exhibit better crystallinity and blue shift when compared to (conventional) CaCO 3 . The present work reveals that the eggshell can be used directly as a catalyst and as resources to synthesize the value-added materials. Eggshells and their byproducts could also be used as biomaterials and host for photoluminescence instead of commercial CaCO 3 .