gneiss

American  

[nahys] / naɪs /

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.

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gneiss British  

/ naɪs /

noun

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

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gneiss Scientific  

/ nīs /

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.

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Other Word Forms

• gneissic adjective

Etymology

Origin of gneiss

Borrowed into English from German around 1750–60

Compare meaning

How does gneiss compare to similar and commonly confused words? Explore the most common comparisons:

• gneiss vs. granite
• schist vs. gneiss

Example Sentences

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

These crystalline changes create identifying textures, which is shown in the figure below comparing the phaneritic texture of igneous granite with the foliated texture of metamorphic gneiss.

From Textbooks • Jan. 1, 2017

They reach 1000 ft. in thickness, occupying undulating hollows in the underlying gneiss, and dip towards the Noursoak Peninsula at 20�, when the overlying Atanakerdluk strata come in.

From Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 5 "Greek Law" to "Ground-Squirrel" by Various