Gneiss is a type of metamorphic rock. The minerals in gneiss may come from rocks which were originally either igneous or sedimentary. They were heated and squeezed, and the minerals recrystallized.
The Lewisian complex or Lewisian Gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane. These rocks are of Archaean and Palaeoproterozoic age, ranging from 3.0–1.7 Ga.
- Blatt, Harvey, Robert J. Tracy & Ernest G Ehlers 1996. Petrology : igneous, sedimentary, and metamorphic. Freeman, New York.
- Ga = thousands of millions of years ago; so 1.7 Ga = 1,700,000,000 years ago