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gneiss

American

[nahys] / naɪs /

noun

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 British

/ naɪs /

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

gneiss Scientific

/ nīs /

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

Etymology

Origin of gneiss

Borrowed into English from German around 1750–60

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Vocabulary lists containing gneiss

Rocks and Minerals - Middle School and High School

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Example Sentences

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The company is now training modern exploration techniques on outcroppings of a 1.8-billion-year-old type of metamorphic rock called Pinto gneiss.

From Los Angeles Times • Mar. 30, 2026

The oldest rock with a reliable age—a gneiss from Canada—is 4.03 billion years old.

From Science Magazine • Apr. 30, 2024

In front of me, a sheer wall of stippled gneiss.

From New York Times • Aug. 22, 2022

The sequence slate → phyllite → schist → gneiss illustrates an increasing metamorphic grade.

From Textbooks • Jan. 1, 2017

The steep, final cone of the rock consists of a granulitic gneiss of varying texture from coarse to fine, and abounding in garnets.

From Narrative of the Circumnavigation of the Globe by the Austrian Frigate Novara, Volume I (Commodore B. Von Wullerstorf-Urbair,) Undertaken by Order of the Imperial Government in the Years 1857, 1858, & 1859, Under the Immediate Auspices of His I. and R. Highness the Archduke Ferdinand Maximilian, Commander-In-Chief of the Austrian Navy. by Scherzer, Karl Ritter von

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023