Orthogneiss

**Petrology:** Orthogneiss has a granite composition and exhibits a characteristic banded deformation structure. The light bands consist of recrystallized aggregates of quartz, potassic feldspar and plagioclase. Dark bands are enriched in biotite. Accessory minerals are zircon and apatite.

**Genesis:** This sample of orthogneiss has an original granite protolith, which was formed by crystallization of magma generated during rifting between the Cambrian and Early Ordovician periods (approximately 520 million years ago). The deformation and metamorphism was caused during the Variscan orogeny (350–330 million years ago).

## Keywords
stone