The Collaborative International Dictionary of English v.0.48:

Schist \Schist\ (sh[i^]st), n. [Gr. ? divided, divisible, fr. ?
   to divide: cf. F. schiste. See Schism.] (Geol.)
   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]

WordNet (r) 3.0 (2006):

schist
    n 1: any metamorphic rock that can be split into thin layers

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "schist":
   aa, abyssal rock, basalt, bedrock, block lava, brash, breccia,
   conglomerate, crag, druid stone, festooned pahoehoe, gneiss,
   granite, igneous rock, lava, limestone, living rock, magma,
   mantlerock, metamorphic rock, monolith, pahoehoe, pillow lava,
   porphyry, pudding stone, regolith, rock, ropy lava, rubble,
   rubblestone, sandstone, sarsen, scoria, scree, sedimentary rock,
   shelly pahoehoe, stone, talus, tufa, tuff