This sample of limestone is from the Steinheim crater, in southern Germany. On one surface of the sample, concial, ‘horse tail’ fracture surfaces known as shatter cones can be observed. Shatter cones are formed as the impact shock-wave travels through the target rock. The mechanism by which they form is still debated, but as the shock wave passes through the target rock it interacts with small asperities or inclusions creating a concial fracture surface down-stream of the shock. Shatter cones can therefore be used to determine the direction the shock wave was travelling: where the cone points towards the shock source, typically assumed to be the crater. Shatter cones require very high pressure shock waves to form, and so far have only been found around impact craters, nuclear weapons test sites, and high pressure shock wave experiments.
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