of the cones repeating cone-on-cone, at various scales in the same sample. They are only known to form in rocks beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the range of 2-30 GPa. Occurrence The effects described above have been found singly, or more often in combination, associated with every impact structure that has been identified on Earth. The search for such effects therefore forms the basis for identifying possible candidate impact structures, particularly to distinguish them from volcanic features. See also Impactite Meteorite shock stage Suevite References External links Chapter 4, 'Shock-Metamorphic Effects in Rocks and Minerals' of the online book, French, B.M. 1998. Traces of Catastrophe, A handbook of shock-metamorphic effects in terrestrial meteorite impact structures, Lunar and Planetary Institute 120pp. Shock metamorphism page. Shatter cones page. Impact geology Metamorphic petrology Glass in nature