Named stone
Mount Rogers rhyolite
Also called Mount Rogers metarhyolite, Mt. Rogers rhyolite
A kind of rhyolite, felsite and metavolcanic rock
Mount Rogers rhyoliteRhyolite, felsite and metavolcanic rockMid-AtlanticDescription
Mount Rogers rhyolite is the metamorphosed volcanic rock of Virginia's highest mountain, in Grayson and Smyth counties in the far southwest of the state. It is gray to purple (the USGS calls the porphyritic rhyolite very dusky purple), with white or pink crystals scattered through a fine groundmass. Some pieces are aphanitic, others granular, and crystals over 5 mm can make up as much as 40 percent of the rock, yet it breaks straight across them as if they were not there. The rhyolites erupted about 760 to 749 million years ago, when the continent was rifting. People may have used it from the Early Archaic, used it most in the Middle and Late Archaic, and kept using it in the Woodland period, but it did not travel far from Grayson County.
How to identify it
- Colour
- Gray to purple, with white or pink phenocrysts (Virginia DHR); the porphyritic rhyolite is mapped as very dusky purple (USGS).
- Texture
- Fine-grained and aphanitic to granular; phenocrysts larger than 5 mm can make up to 40 percent of the rock; fractures pass through the phenocrysts.
- Inclusions
- Quartz and mesoperthite (feldspar) phenocrysts, about 30 percent in the porphyritic rhyolite (USGS).
Geology
Neoproterozoic Mount Rogers Formation (Crossnore Complex) of the Blue Ridge in Virginia, North Carolina and Tennessee. Its rhyolite lava flows and welded tuffs are dated by zircon to about 760-749 million years, from continental rifting. Members include the Fees, Buzzard Rock, Whitetop and Wilburn rhyolites. The rock was later metamorphosed.
Where it comes from
Mid-Atlantic, Southeast
States
Quarries and outcrops
- Mount Rogers area, Grayson and Smyth counties, Virginia (site 44GY0018 for the DHR sample)
Used by
- Possibly Early Archaic; heaviest use in the Middle and Late Archaic; continued into the Woodland (Virginia DHR)
Sources
- Tolley. 1999 (updated 2023). Mount Rogers Rhyolite. Virginia Department of Historic Resources, Projectile Points and Lithics guide.dhr.virginia.gov (opens in a new tab)
- U.S. Geological Survey. Mount Rogers Formation - Porphyritic rhyolite (VAZmp), State Geologic Map Compilation unit description.mrdata.usgs.gov (opens in a new tab)
- U.S. Geological Survey. Geolex: Mount Rogers Formation.ngmdb.usgs.gov (opens in a new tab)
- Merschat, Arthur J., Ryan J. McAleer, Christopher S. Holm-Denoma and C. Scott Southworth. 2023. Geology of the Mount Rogers area, revisited: Evidence of Neoproterozoic continental rifting, glaciation, and the opening and closing of the Iapetus Ocean, Blue Ridge, VA-NC-TN. Conference paper (USGS publication record).usgs.gov (opens in a new tab)