Gneiss
[naɪs]
Definition
(n.) A crystalline rock, consisting, like granite, of quartz, feldspar, and mica, but having these materials, especially the mica, arranged in planes, so that it breaks rather easily into coarse slabs or flags. Hornblende sometimes takes the place of the mica, and it is then called hornblendic / syenitic gneiss. Similar varieties of related rocks are also called gneiss.
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Definition
n. (geol.) a species of stratified rock composed of quartz feldspar and mica.—adjs. Gneiss′oid having some of the characters of gneiss; Gneiss′ose having the structure of gneiss.
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