<p>Rheological behavior of clay can cause major engineering disasters such as foundation instability and slope sliding. Mineral composition is a key factor influencing the rheological properties of clay. This study explores the mechanisms and action principles of clay rheology, and deepens the quantitative analysis of the influence of mineral composition on rheological properties. Based on experimental studies of the influence of different mineral compositions on rheological properties, it is found that components such as clay minerals and organic matter form a highly viscous substance with microstructural characteristics, which has a decisive influence on rheological properties; this substance is termed rheological matter. Experiments further revealed that the distribution and morphology of the rheological matter affect the rheological properties of clay. As the uniformity of the distribution of the rheological matter increases, the viscosity coefficient of the clay rheology tends toward a certain stable value, becomes unrelated to the distribution and morphology of the rheological matter, and depends solely on the content and properties of the rheological matter. This discovery regarding the pattern of influence of rheological matter on clay rheology clarifies the material origin of clay rheology, deepens the understanding of its physical nature, extends the analysis of the influence of mineral composition toward quantitative mechanistic analysis, and contributes to mitigating major engineering disasters induced by soil rheology from their root causes.</p>