Simplify the following text for a Grade 9 native English-speaking person.
Original: Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks .
Simplified: Gneiss is a type of metamorphic rock . The minerals in gneiss may come from rocks which were originally either igneous or sedimentary .