type of fine-grained sedimentary rock which splits readily into thin plates, 1747, possibly a specialized use of Middle English schale "shell, husk, pod" (late 14c.), also "fish scale," from Old English scealu (see shell (n.)) in its base sense of "thing that divides or separates," in reference to the way the rock breaks apart in layers. Compare Middle English sheel "to shell, to take off the outer husk" (late 15c.). The geological use also perhaps was influenced by German Schalstein "laminated limestone," and Schalgebirge "layer of stone in stratified rock," from the German cognate Schale "a scale, shell, husk, a slice, a thin layer."
updated on August 06, 2022