Mount Rogers Formation - Phenocryst-poor rhyolite (VAZmr;0)

State	Virginia
Name	Mount Rogers Formation - Phenocryst-poor rhyolite
Geologic age	Proterozoic Z
Original map label	Zmr
Comments	In Grayson, Washington, and Smyth Counties only; Blue Ridge Anticlinorium, Southwest. From expanded explanation (ref. VA002): Phenocryst-poor rhyolite (Whitetop Rhyolite Member and Buzzard Rock Member, Mt. Rogers volcanic center). Whitetop Rhyolite Member, phenocryst-poor, very dusky purple, high-silica, metaluminous rhyolite lava fl ows and minor tuff containing 0 to 10 percent phenocrysts of quartz and mesoperthite. Buzzard Rock Member, blackish-red, low-silica, metaluminous rhyolite lava flows containing 5 to 20 percent prominant phenocrysts of mesoperthite and plagioclase; includes minor interbedded volcaniclastic sedimentary rocks. The Buzzard Rock is a thin unit that occurs beneath the Whitetop Rhyolite Member.
Primary rock type	rhyolite
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanic > Rhyolite
Map references	Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Unit references	Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000 Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Geographic coverage	Grayson - Smyth - Washington