Definition
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Etymology
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Very fine grained fault rock which is composed of glassy matrix that often contains inclusions of wall-rock fragments.
From pseudo- + tachylite, a glassy rock generated by frictional heat within faults.
Fine Grained Rock, Opaque Rock
Greywacke is defined as a dark coarse-grained sandstone rock which contains more than 15 per cent clay
From German Grauwacke, from grau grey + wacke
Fine Grained Rock, Opaque Rock