Or pseudotachylite, dark brittle fault rock occurring in veins and fractures in host rocks with low porosity. Pseudotachylyte is thought to form by local melting of a host rock along a fault in response to seismic activity on the fault and associated local generation of frictional heat. The name was derived from ‘tachylyte’ (basalt glass) occurring in settings that could not be explained by igneous activity
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