Petersburg Granite

Light- to dark-gray to pink, fine- to coarse-grained, equigranular to porphyritic, foliated to nonfoliated, ranges from granite to granodiorite in composition; multiple intrusive phases are present. The granite contains xenoliths of biotite gneiss and amphibolite. Mineralogy: quartz + sodic plagioclase + potassium feldspar + biotite ± hornblende; accessory minerals include ilmenite, magnetite, pyrite, zircon, apatite, titanite, muscovite, and fluorite (Goodwin, 1970; Daniels and Onuschak, 1974; Wright and others, 1975). Current mapping restricts the Petersburg Granite to a contiguous unit that crops out in the Cities of Richmond and Petersburg; this roughly corresponds to one of four discrete plutons mapped as Petersburg Granite on the 1963 Geologic Map of Virginia. Samples from within this pluton were dated at 330±8 Ma (U-Pb zircon; Wright, and others, 1975). The northwestern edge of the pluton is mylonitized along the Hylas fault zone (Bobyarchick and Glover, 1979).
State Virginia
Name Petersburg Granite
Geologic age Mississippian
Lithologic constituents
Major
Igneous > Plutonic > Granitic > Granite
Comments Southeastern Piedmont
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 Chesterfield - Dinwiddie - Goochland - Hanover - Henrico - Sussex - Colonial Heights - Petersburg - Richmond