File:Augen gneiss (Ravensford, Great Smoky Mountains National Park, North Carolina, USA) 1 (41066265425).jpg

Augen gneiss from the Precambrian of North Carolina, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

Gneiss is a high-grade, foliated metamorphic rock that consists of alternating bands of light- and dark-colored minerals (often quartz and biotite mica, as in the sample shown here). Notice the numerous, discrete, somewhat eye-shaped masses of light-colored quartz in the photo. Gneiss having such mineral masses is called "augen gneiss" ("augen" is German for "eyes").

The rock is from the Blue Ridge Physiographic Province. The Appalachian Mountains of eastern America consist of three provinces: the Valley & Ridge, the Blue Ridge, and the Piedmont. A couple of American national parks have been established in the most scenic stretches of the Blue Ridge: Great Smoky Mountains and Shenandoah. The Blue Ridge is mostly composed of Precambrian basement rocks (igneous & metamorphics). The mountains of the Blue Ridge are generally rounded and not very tall. This is unlike the tall, mostly sharp-peaked mountains of western America's Cordillera, the Andes of South America, the Alps of Europe, and the Himalayas of Asia. Compared with those geologically young mountain chains, the Blue Ridge is relatively old - the Appalachians have been subjected to long term erosion for about one-third of a billion years.