Poromechanical and Crack Evolution of Olivine‐Rich Rock During Serpentinization

Abstract Serpentinization alters the strength, fracture behavior, and rheology of ultramafic rocks, yet the coupled evolution of mineral reactions, cracking, and mechanical softening remains poorly constrained. We experimentally simulated serpentinization in dunite at 220°C and 15 MPa for 14 and 30 days and compared the reacted specimens with dry heat‐treated controls. Poromechanical tests and petrophysical measurements showed that serpentinization reduced the drained and unjacketed bulk moduli by up to 50% after 30 days. X‐ray diffraction (XRD) confirmed progressive olivine‐to‐serpentine replacement associated with solid‐volume expansion, while micro‐CT imaging captured reaction‐driven microcrack initiation and propagation. Crack‐density analysis showed that serpentinization generates microcracks but also partially seals larger features through secondary mineral growth, consistent with mercury intrusion porosimetry results. These results reveal a coupled process in which serpentinization simultaneously produces and infills fractures, reshaping the rock's mechanical framework. The findings clarify mechanisms governing seismic velocity reductions and hydromechanical weakening in serpentinizing mantle environments.