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Talc is an important industrial mineral with a broad range of applications. Particle size and crystal structure have a significant influence on the potential uses. The present study examined the influence of grinding and ultrasound treatment on talc from a new deposit, Gemerská Poloma, in Slovakia. The general knowledge that grinding produces progressive structural disorder leading to amorphization, whereas sonication has a negligible effect on the talc crystal structure, was confirmed by X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). Partial reduction of particle size along with delamination was observed by XRD after sonication, low-angle laser light scattering (LALLS), scanning electron microscopy (SEM), and TEM. The specific surface area (SSA) increased slightly after prolonged sonication, but grinding initially caused a rapid increase in SSA followed by a drastic decrease after prolonged grinding time of up to 120 min which was attributed to the aggregation of amorphized talc. Sonication and grinding had different influences on the thermal behavior of the talc studied. Sonication decreased slightly the dehydroxylation temperature, whereas grinding added a significant mass loss at low temperature, arising from the dehydration of hydrated Mg cations released from the talc structure during amorphization. The initial high whiteness value of talc decreased slightly after grinding or sonication. Thermogravimetry was suggested as a useful tool to track and predict changes in the talc structure upon sonication and grinding.