The Geology of Virginia

A Resource for Information on the Commonwealth's Geology

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HylasZoneMylonite

Hylas Zone Mylonite

This micrograph illustrates a mylonite from the Hylas Zone in the eastern Piedmont ~5 km west of Doswell, Virginia.  The rock is characterized by a well-developed foliation with elongate quartz ribbons (transparent grains) and feldspar porphyroclasts.  The rock originally was a granodiorite that was strongly deformed and sheared, under ductile conditions, into a mylonite. Checkout […]

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What’s New in Virginia Geology

VAlavas

Virginia is for Lavas- The Catoctin Formation

Many of the highest peaks in Shenandoah National Park (including Hawksbill, Stony Man, and Hightop Mountain, just to name a few) are underlain by distinctive bluish-green rocks that were once ancient lava flows (Virginia is for Lavas!), and are part of a geologic unit known as the Catoctin Formation.  From the presidential retreat at Camp David to Jefferson’s […]

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