|any coarse-grained metamorphic rock that is banded and foliated: represents the last stage in the metamorphism of rocks before melting|
|[C18: from German Gneis, probably from Middle High German ganeist spark; related to Old Norse gneista to give off sparks]|
|gneiss (nīs) Pronunciation Key
A highly foliated, coarse-grained metamorphic rock consisting of light-colored layers, usually of quartz and feldspar, alternating with dark-colored layers of other minerals, usually hornblende and biotite. Individual grains are often visible between layers. Gneiss forms as the result of the regional metamorphism of igneous, sedimentary, or other metamorphic rocks.