schist(n = noun.substance) - any metamorphic rock that can be split into thin layers;
is a kind of metamorphic rock
Any crystalline rock having a foliated structure (see Foliation) and hence admitting of ready division into slabs or slates. The common kinds are mica schist, and hornblendic schist, consisting chiefly of quartz with mica or hornblende and often feldspar. [1913 Webster]
schist, n. a foliated metamorphic rock composed of layers of different minerals and splitting into thin irregular plates.
Derivative:
schistose adj.
Etymology:
F schiste f. L schistos f. Gk skhistos split (as SCHISM)