Clay minerals are essential components of clay rocks and soils, forming the primary constituents of various terrestrial surface coverings. Studying their structural attributes, particle dimensions, and moisture content variations is crucial for understanding environmental dynamics in clay mineral-rich regions and guiding mineral industry applications. Due to diverse geological applications and practical requirements, traditional mineral characterization methods often have limited applicability for mining minerals with distinct physical properties. Terahertz spectroscopy technology, a novel non-contact coherent testing method, utilizes fingerprint spectra, wide spectra, and water sensitivity within this frequency band. This technology enables the non-destructive detection of clay minerals, providing optical information to differentiate their crystal structure and composition. This article primarily focuses on using terahertz time-domain spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy to study the thermal decomposition characteristics of clay minerals. The composition, particle size, and calcination products of kaolin, a vital raw material significantly influence the quality of ceramics. Experimental results confirm substantial variations in the absorption coefficient and refractive index of different states of kaolin within the terahertz frequency range. Differences in the crystal structure of talc and vermiculite, belonging to the 2∶1 type layer silicate, result in significant disparities in their terahertz spectra, effectively indicating thermal decomposition byproducts and moisture content in conventional electrically neutral hydrous minerals. Contrary to conventional understanding, vermiculite exhibits peaks at 1.10 THz without chemical interventions. The appearance of this can facilitate substance characterization and advance optical devices while enhancing the understanding of minerals in terahertz spectroscopy. This offers a fresh research perspective for the interdisciplinary investigation of terahertz spectroscopy and geology.