schist (n.)

type of layered metamorphic rock, 1795 (earlier schistus, c. 1600), from French schiste (16c.), from Latin schistos lapis "stone that splits easily" (Pliny), from Greek skhistos "divided, separated," from skhizein "to split" (from PIE root *skei- "to cut, split"). The rock splits easily in layers. Liddell & Scott say Greek skhistos lithos was "probably talc."