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

/ 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.

Derived Forms

• ˈgneissic, adjective

Other Words From

• gneissic 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

Example Sentences

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

From Science Magazine

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

From New York Times

The ridges are gneiss and schist; the valleys, marble, worn down through various glaciation events.

From New York Times

Stories, in that sly way, are his thing, and in his daily life he’s not averse to mussing around with geological terms like “hornfels” and “gneiss.”

From New York Times

The dark, blocky cylinder appears to comprise a roughly fifty–fifty mix of ice and a metamorphic rock called gneiss, Talalay says.

From Nature