Fig. 3

Secondary electron images of microstructures in novaculite and wear material, collected with JEOL 8900 microprobe at McGill University (beam current = 20 kV). Images a and c–f are of experiment 97. Image b is of experiment 101. a Surface of unsheared novaculate (starting material) with empty (100 µm) pores. b Cross-sectional view of wear material layer. White arrows indicate thin slip zones composed of compressed powder. c View normal to slip surface (ss) that was opened by separating novaculite cores. Clumps of ellipsoidal powder grains decorate surface and adhere to striated slip surface. Uneven distribution of wear material leaves exposed patches of slip surface with remaining 10 µm pores. d Nanopowder (np) compressed into striated plates (sp) parallel to slip direction. e Broken fragments of striated plates, interlayered with nanopowder, displaying development and cataclasis of multiple slip surfaces during single shear experiment. f Closeup on wear powder showing quartz chips, 10 µm clumps, and 1 µm particles. Bright clusters show debris from clumps which exploded during observation