Alligator Back Formation (VACAZab;0)

State	Virginia
Name	Alligator Back Formation
Geologic age	Proterozoic Z-Cambrian
Original map label	[Zab
Comments	Western Piedmont, Sauratown Mountains. From expanded explanation (ref. VA002): Alligator Back Formation (Sauratown Mountains; Conley, 1985). Light-gray, medium- to coarse-grained porphyroblastic garnet-mica schist; contains interbeds of dark-gray graphitic mica schist, calc-gneiss, mica gneiss, feldspathic quartzite with blue quartz granule beds, and garnet-hornblende schist. Mineralogy: (1) quartz + muscovite + garnet + staurolite + biotite + magnetite; (2) quartz + muscovite + biotite + garnet + kyanite + staurolite + magnetite; (3) quartz + biotite + muscovite + garnet + chlorite + epidote + rutile + titanite + magnetite-ilmenite (retrograde assemblage locallized in sheared rocks along the Ridgeway fault). Garnet, kyanite, and staurolite porphyroblasts are generally pristine.
Primary rock type	mica schist
Secondary rock type	amphibolite
Other rock types	gneiss; quartzite
Lithologic constituents	Major Metamorphic > Schist > Mica-schistmica schist Minor Metamorphic > Gneiss Metamorphic > Amphibolite Incidental Metamorphic > Metasedimentary > Metaclastic > Quartzite
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	Henry - Pittsylvania