A type of hard, coarse sandstone made of dark minerals and rock fragments, commonly found in mountain regions.
From German Grauwacke, where grau means 'gray' and wacke comes from a Low German dialect word for 'rock' or 'stone.' The term was adopted by English geologists from German geological terminology.
Geologists borrowed this German name wholesale because German scientists had done so much early rock classification—you'll see lots of German geology terms in English because they literally invented the science of reading rocks.
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