Alligator Back Formation

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.
State Virginia
Name Alligator Back Formation
Geologic age Proterozoic Z-Cambrian
Lithologic constituents
Major
Metamorphic > Schist > Mica-schist
Minor
Metamorphic > Amphibolite
Metamorphic > Gneiss
Incidental
Metamorphic > Metasedimentary > Metaclastic > Quartzite
Comments Western Piedmont (Sauratown Mountains)
References

Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.

NGMDB product
Counties Henry - Pittsylvania