Wacke
Origin
Middle High German wacke "boulder," from Old High German waggo or wacko, yielding German Wacke, probably cognate with Old High German wegan "to move"
Online Etymology Dictionary http://www.etymonline.com/index.php?search=wacke&searchmode=none
Full definition of wacke
Noun
wacke
(countable and uncountable; plural wackes)- (geology) A soft, earthy, dark-coloured rock or clay derived from the alteration of basalt.