Noun
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.
Source: Webster's dictionaryBirlinn. p. 93 state of the Lewisian gneiss bedrock of much of the Outer Hebrides that "these rocks are amongst the oldest to be found anywhere on the planet". Source: Internet
During the initial collision of the Asia and Indian plates, this granitic batholith was buried to depths of about convert or more, highly metamorphosed, highly deformed, and partially remelted during the Eocene Period to form gneiss. Source: Internet
Geologically, the island consists of gneiss and argillaceous schists with occasional tufts and other sedimentary layers from which fossils have been recovered. Source: Internet
It consists of sillimanite K-feldspar grade schist and gneiss intruded by numerous sills and dikes of leucogranite ranging in thickness from 1 cm to 1,500 m (0.4 in to 4,900 ft). Source: Internet
Not all gneiss rocks have detectable banding. Source: Internet
Orthogneiss from the Czech Republic Gneissose rocks have properties similar to gneiss. Source: Internet