wacke (n.)

rock resembling sandstone, 1803, from German Wacke, from Middle High German wacke "large stone, rock projecting from the surface of the ground," from Old High German wacko, waggo "gravel, pebble, rock rolling in a riverbed," which probably is from Old High German wegan "to move," from Proto-Germanic *wag- "to move about," from PIE root *wegh- "to go, move." A miner's word, brought into geology by German geologist Abraham Gottlob Werner (1750-1817).