A fissile rock composed mostly of layers of clay-like, fine-grained
→ sediments. Shale is the most frequently occurring
→ sedimentary rock.
Probably from obsolete or dialect shale "scale, shell," from M.E., from
O.E. scealu, → rock.
Ardavâl "shale," in the dialectal Mod.Pers. of Golpâyegân, Arâk, Xonsâr, etc.
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