A Resource for Information on the Commonwealth's Geology
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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 […]
What’s New in Virginia Geology
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 […]