Metagabbro. (southwestern Piedmont, Conley, 1985). Dark-green and white, massive to layered, coarse-grained equigranular metagabbro. Mineralogy: clinopyroxene + orthopyroxene ± garnet + hornblende + plagioclase + magnetite. Garnets are surrounded by thin coronas composed of plagioclase and symplectic intergrowths of plagioclase-pyroxene. Forms elongate concordant bodies intrusive into the Bassett Formation. (northern Piedmont, Drake and Froelich, in press). Greenish-gray, fine- to coarse-grained, well-foliated epidote plagioclase-hornblende amphibolite; locally contains relict clinopyroxene. Occurs as sills in the Mather Gorge Formation. Fisher (1971) reports that zircons from an amphibolite body on an island in the Potomac River have a Pb-Pb age of 525+/- 60 Ma, and a concordia age of 550 Ma, assuming continuous diffusion; a Cambrian age for metagabbroic sills in the Mather Gorge would be consistent with regional geologic relations.
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.