- a rock of fissile or laminated structure formed by the consolidation of clay or argillaceous material.
- a dark fine-grained laminated sedimentary rock formed by compression of successive layers of clay-rich sediment
n.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 separate,” in reference to the way the rock breaks apart in layers. Cf. Middle English sheel “to shell, to take off the outer husk” (late 15c.). Geological use also possibly influenced by German Schalstein “laminated limestone,” and Schalgebirge “layer of stone in stratified rock.”
- A fine-grained sedimentary rock consisting of compacted and hardened clay, silt, or mud. Shale forms in many distinct layers and splits easily into thin sheets or slabs. It varies in color from black or gray to brown or red.
A sedimentary rock formed from layers of clay.