[nahys] 
| a metamorphic rock, generally made up of bands that differ in color and composition, some bands being rich in feldspar and quartz, others rich in hornblende or mica. |
| gneiss (nīs) n. A banded or foliated metamorphic rock, usually of the same composition as granite. [German Gneis, probably alteration of Middle High German ganeist, spark (from its appearance), from Old High German gneista.] gneiss'ic (nī'sĭk), gneiss'oid' (nī'soid'), gneiss'ose' (nī'sōs') adj. |
| 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. |