File:Augen gneiss (Precambrian; Rt. 93 roadcut next to the New River, Mouth of Wilson, Virginia, USA) 4 (30112152173).jpg

Augen gneiss in the Precambrian of Virginia, USA. (geology hammer for scale)

Gneiss is a high-grade, foliated metamorphic rock that consists of alternating bands of light- and dark-colored minerals (often quartz and biotite mica). The surface shown above consists of Precambrian-aged gneiss. The surrounding outcrop is gneiss with some shear zones and minor faults. Some epidote is present in bands and small pods.

Notice the eye-shaped masses of quartz in the middle part of the photo. Gneiss with roughly eye-shaped mineral masses is called "augen gneiss" ("augen" is German for "eyes").

This site in Virginia is part of 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.