Earthquakes jar at the macroscopic level: Ground ruptures; houses shake. But their effects can also be discerned at the nano level. Crushed wear material between rock faces that slip past each other develop patches of mirrorlike areas characterized by nanostructures. Investigating the effect in limestone, researchers led by Berend A. Verberne and Christopher J. Spiers of the Netherlands’ Utrecht University have now found that nanoparticles 5–20 nm in diameter cluster into spherules, which in turn align into nanofibers oriented along the slip direction (Science 2014, DOI: 10.1126/science.1259003). The nanofiber patches are small—10–100-µm wide—and can form with as little as 5-mm rock displacement under typical earthquake-related pressures. The changes in the rock are a product of the energy put into the system, Verberne says. And the movement of the nanoparticles and their alignment into the fibers could play an important role in how the rocks slip. Although Verberne and colleagues only studied limestone, the mirrorlike patches are found in other rock types, suggesting a general mechanism may be at work.