Robertson River Igneous Suite - Amissville alkali feldspar granite

Light- to dark gray, medium-grained, inequigranular to porphyritic (quartz phenocrysts) alkali feldspar granite composed of microcline mesoperthite, quartz, and plagioclase, with aegirine, riebeckite, biotite, zircon, fluorite, and stilpnomelane. Euhedral quartz phenocrysts are diagnostic; locally displays miarolitic cavities containing quartz; intruded by fine-grained dikes of identical mineralogic composition. Field relations indicate the Amissville is older than Battle Mountain granitoid; geochemistry indicates these units are comagmatic.
State Virginia
Name Robertson River Igneous Suite - Amissville 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 - Rappahannock