Schist

Webster's Practical Dictionary- A Practical Dictionary of the Englih Language · 1884 · p. 378

shist, n. (Geol.) A rock having a schistose structure, — used esp. of some kinds of metamorphic rocks. — Schistose'', -os', Schisfous, -us, a. Admitting of division by natural cleavage into flags, slabs, or slates, — used esp. of metamorphic rocks.