Epidote in gneiss in the Precambrian of Virginia, 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). The surface shown above consists of Precambrian-aged gneiss with epidote, which occurs at this site in occasional bands and small pods. Epidote is a greenish-colored silicate mineral (Ca2(Al,Fe)3(SiO4)3(OH) - calcium hydroxy-aluminoferrosilicate).
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.
Locality: Mouth of Wilson Outcrop - roadcut on the northeastern side of Rt. 93, immediately south of the New River bridge, east of the town of Mouth of Wilson, near the southern margin of Grayson County, southwestern Virginia, USA
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