Robertson River Igneous Suite - Arrington Mountain alkali feldspar granite

Light gray, medium-grained, equigranular alkali feldspar granite composed of microcline microperthite, quartz, and plagioclase, with hastingsitic amphibole, biotite, stilpnomelane, allanite, fluorite, zircon, epidote, apatite, rare garnet, and muscovite. The granite is locally intruded by light-gray, fine-grained dikes of mineralogically identical alkali feldspar granite. The unit has been dated at 730± 4 Ma (U-Pb zircon; Tollo and Aleinikoff, in press).
State Virginia
Name Robertson River Igneous Suite - Arrington Mountain alkali feldspar granite
Geologic age Proterozoic Z
Lithologic constituents
Major
Igneous > Plutonic > Granitic > Granite
Comments Blue Ridge Basement Complex, Late Proterozoic Igneous
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 Culpeper - Madison - Rappahannock