Mount Rogers Formation - Porphyritic rhyolite (VAZmp;0)

State	Virginia
Name	Mount Rogers Formation - Porphyritic rhyolite
Geologic age	Proterozoic Z
Original map label	Zmp
Comments	In Grayson, Washington, and Smyth Counties only; Blue Ridge Anticlinorium, Southwest. From expanded explanation (ref. VA002): Porphyritic rhyolite (Wilburn Rhyolite Member, Mt. Rogers volcanic center). Very-dusky-purple, high-silica rhyolitic welded tuff containing about 30 percent quartz and mesoperthite phenocrysts. This unit constitutes a chemically and mineralogically-zoned ash-flow sheet at least 760 m thick, in which the main body is metaluminous and the basal phenocryst-poor 30 m were initially peralkaline.
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 - expanded explanation: 2003, Commonwealth of Virginia, Department of Mines, Minerals, and Energy, Divsion of Mineral Resources, Publication 147, 85 pp 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