Hertzian cone
A Hertzian cone is cone of force that propagates through a brittle, amorphous or cryptocrystalline solid material from a point of impact, eventually removing a full or partial cone; this result is familiar to anyone who has seen what happens to a plate-glass window when struck by a small object, such as an airgun projectile. This is the physical principal that explains the form and characteristics of the flakes removed from a core of tool stone during the process of lithic reduction.
This phenomenon is named after the German physicist Heinrich Rudolf Hertz, who first described this type of wave-front propogation through various media.
See also: Conchoidal fracture