gneiss

[nahys]

noun

1. 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

/ naɪs /

noun

1. any coarse-grained metamorphic rock that is banded and foliated: represents the last stage in the metamorphism of rocks before melting

gneiss

1. 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.

Other Word Forms

• gneissic adjective

Word History and Origins

Origin of gneiss¹

Borrowed into English from German around 1750–60

Word History and Origins

Origin of gneiss¹

C18: from German Gneis, probably from Middle High German ganeist spark; related to Old Norse gneista to give off sparks