GNEISSES

Noun

gneisses

plural of gneiss

Source: Wiktionary

GNEISS

Gneiss, n. Etym: [G.] (Geol.)

Definition: 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 or syenitic gneiss. Similar varieties of related rocks are also called gneiss.

Source: Webster’s Unabridged Dictionary 1913 Edition