Mechanical Properties and Fracture Behaviour of New Zealand Nephrite Jade (Pounamu): Implications for Fibre‐Toughening Mechanisms in Amphibole Monomineralic Rocks

Results of the first comprehensive quantitative analysis of the mechanical properties of New Zealand nephrite jade (pounamu), including hardness, Young's modulus, fracture toughness and notched flexural strength are reported for seven samples. These samples of exceptional quality were pre‐selected by experienced Māori carvers through a ranking process. Nanoindentation and four‐point bending techniques were used to make the measurements. The measured fracture toughness values (8.51–15.01 MPa m 0.5 ) are the highest ever recorded for nephrite jade worldwide, significantly exceeding previously reported values of 1.9–7.7 MPa m 0.5 . Observed microstructures are consistent with the presence of classical toughening mechanisms typical for fibrous materials such as fibre pull‐out, crack deflection and fibre bridging. However, good‐quality nephrite can exhibit catastrophic failure despite its high fracture toughness, indicating that these mechanisms may contribute to fracture resistance without producing progressive macroscopic failure. Additional microstructural or intrinsic factors may also contribute to its exceptional toughness.