<p>Shales play an important role in subsurface engineering applications, including hydrocarbon extraction, geothermal energy production, and carbon sequestration. However, their mechanical behavior is highly sensitive to environmental factors, particularly water exposure. This study systematically investigates the influence of water soaking on the hardness and hardness anisotropy of three shale types (argillaceous, kerogen-rich, and calcite-rich) using Vickers indentation and confocal microscopy. Our results show that not all shales soften upon water exposure and that the degree of softening after 24&#xa0;h of soaking is strongly composition dependent. Argillaceous and calcite-rich shales exhibit substantial hardness reductions (~ 50% and ~ 30%, respectively), whereas kerogen-rich shale shows no measurable softening. X-ray diffraction analysis indicates no detectable mineralogical changes after soaking, ruling out bulk dissolution and lattice swelling as dominant mechanisms. Instead, we infer the softening to the interfacial weakening associated with muscovite-rich phases. In contrast, the absence of softening observed in the kerogen-rich shale may be explained by the lack of water-induced interfacial weakening. Despite significant softening in the argillaceous and calcite-rich shales, all shales retain pronounced anisotropy between bedding-parallel and bedding-normal directions, indicating that the underlying deformation behavior remains largely unchanged after water soaking. These findings provide new insight into the role of mineralogical composition in governing shale mechanical response to water exposure and can help guide the modeling of shale behavior in moist subsurface environments.</p>