The crack patterns of glass which form when a propagating crack intersects a free surface are considered in terms of the (G,R) vs DELTA C universal energy diagram for crack growth after Broek (1974). After briefly reviewing its derivation, the diagram is applied to glass fracture and the bifurcation of cracks in glass. The concepts are then extended to address the formation of the mirror/mist boundary on glass fracture surfaces. Features of the (G,R) vs DELTA C diagram and the KI - V diagram after Richter (2002) are combined to estimate the kinetic energy associated with a crack in soda lime silica glass at its terminal velocity. The kinetic energy is ~ 70% of the total energy requirement for crack growth. Implications regarding other glass fractures, such as the absence of the mirror/mist boundary for nano-whiskers, are also discussed. The (G,R) vs DELTA C approach appears to have far reaching applications in describing glass fractures.
