Microcracks in Basalt and Tonalite at Friction

Abstract

Abstract—The growth rate and size of microcracks formed in the surface layer of basalt and tonalite (granodiorite) at friction are studied using luminescence. It is found that upon breaking of crystal lattices of labradorite and quartz contained in these rocks, triboluminescence signals arise. Each signal corresponds to an embryo microcrack whose surface contains electronically excited free radicals ≡Si–O^–, Fe³⁺ ions, and electron traps. The average growth rate of embryo microcracks in basalt varies from ~0.6 to ~1 km/s and in tonalite, from ~ 0.7 to ~1.3 km/s. The sizes of embryo microcracks in basalt range within ~3 to ~5.5 μm and in tonalite from ~3.5 to ~6.5 μm.