Dataset for: Frictional roles of quartz, albite, and chlorite in wet fault gouge-insights from ultrasonic transmission

Fault gouges in the upper crust are frequently exposed to varying moisture conditions due to natural hydrological circulation and fluid injection, yet the mineralogical origin of their fluid sensitivity remains poorly constrained. We investigate how water modifies the frictional behavior of quartz, albite, chlorite, and a natural fault gouge through velocity-step friction tests under dry and wet conditions. Meanwhile, the ultrasonic transmission was monitored to track particle-scale contact evolution. The results show that quartz provides stable interlocking frameworks, albite exhibits pronounced consolidation via water‑promoted dissolution-reprecipitation, and chlorite undergoes cyclic deformation that enhances interlayer lubrication. Ultrasonic transmitted amplitude effectively captures transient frictional evolution, whereas wave velocity serves as a reliable indicator of elastic contact quality. The frictional response of natural gouge is not a linear superposition of its constituents: dry gouge approximately follows a weighted sum of single-mineral strengths, but wetting disrupts this linearity through coupled mineral interactions. In natural gouge assemblage, quartz sustains structural integrity, albite acts as a binding agent mediated by water‑rock reactions, water serves as the reactive medium, and chlorite maintains lubrication during consolidation of the other phases. Our finding constrains the competing contributions of dissolution‑enhanced strengthening and lubrication‑induced weakening in fluid‑influenced fault zones.