Gneiss is a high-grade metamorphic rock characterized by its distinct foliated texture and banded appearance, known as gneissic banding. It forms under intense heat and pressure, typically deep within the Earth's crust, through the metamorphism of pre-existing igneous or sedimentary rocks such as granite or shale
. Key features of gneiss include:
- Texture: Coarse-grained with mineral grains visible to the naked eye, arranged in alternating light and dark bands or layers due to mineral segregation during metamorphism
- Composition: Mainly composed of quartz, feldspar, and biotite, with possible inclusions of garnet, hornblende, or kyanite depending on the parent rock
- Formation: Results from regional metamorphism, often starting from sedimentary rocks like shale or igneous rocks like granite, undergoing recrystallization without melting
- Classification: Orthogneiss if derived from igneous rocks, paragneiss if from sedimentary rocks
Gneiss is a durable rock widely used in construction and decorative applications due to its hardness and attractive banded appearance
. In summary, gneiss is a foliated, coarse-grained metamorphic rock formed by the high-grade metamorphism of igneous or sedimentary rocks, distinguished by its characteristic layered mineral bands.
