gems, jade, amphibole trade, nephrite, tremolite, actinolite, Switzerland, Canada, Soviet Union, physical properties, fracture toughness

Fracture parameters were measured in jade samples from three different sources, revealing fracture toughness values ranging from 2.9 to 5.5 MN m⁻³ᐟ² and fracture energies between 269 and 986 J m⁻². Jade’s exceptional resistance to crack propagation is attributed to its fibrous microstructure, where individual nephrite fibers, approximately 89 μm in diameter, are grouped into feather-like or cylindrical bundles arranged in a randomly oriented, woven structure. Sub-critical crack growth can occur in the presence of water but not in lapping oil. The fracture behavior of jade is also compared to that of common rocks and engineering ceramics, highlighting its unique toughness.