Leucocratic metagranite. White to light-olive-gray, to pink, fine- to medium-grained, massive monzogranite composed of 22 to 38 percent quartz (white, clear, or blue), 33 to 34 percent orthoclase, microcline, and rod and bleb microperthite, and 38 to 44 percent oligoclase and albite, and minor biotite. Locally, potassium feldspar porphyroblasts are 1 to 2 cm in diameter. In Loudoun County this unit becomes coarser-grained and richer in biotite from west to east across the outcrop belt. U-Pb zircon data from two localities in Loudoun County indicate crystallization ages of 1058±3 Ma and 1060±2 Ma (Aleinikoff and others, 1993).
Blue Ridge Basement Complex, Middle Proterozoic (Grenville-Age) Plutonic Rocks
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.