Gneis

Part of speech: noun

Definitions

1. A metamorphic rock composed primarily of granular textures made up of quartz, feldspar, and mica that forms under high temperature and pressure conditions
2. A type of rock characterized by its banded appearance and composition, typically formed from the alteration of igneous rock through metamorphic processes
3. A foliated rock known for its distinctive layering and mineral distribution, commonly formed in the Earth's crust by tectonic plate movements

Etymology: German miners used "Gneis" for a rock that glints when struck or split, and English borrowed the word from them. The name points to the rock's sparkle, from a Middle High German root meaning something like "spark." Its exact path from that root is uncertain, but the glinting-stone sense is the key to the name. The rock itself is a coarse, banded metamorphic rock, formed under heat and pressure, with light and dark mineral layers that often look like stripes. Scientists kept the miners' term because it described what people saw on the surface, and the banding is what makes the stone recognizable at a glance.

Synonyms: gneiss, metamorphic rock, banded rock, granite-like rock