Diorite, light- to dark-gray, fine- to coarse-grained. Hornblendite and amphibolite occur as dikes associated with diorite; these are coarse-grained, with blocky hornblende and plagioclase; epidote-rich alteration zones are common. Mineralogy: hornblende + plagioclase (intermediate composition); accessory minerals include apatite, titanite, zircon, garnet, pyrite, and magnetite. Augite, diopside, quartz, and potassium feldspar are locally present. Hornblende is largely replaced by chlorite or biotite; plagioclase contains abundant epidote inclusions. Late biotite porphyroblasts are common; these are commonly hydrated to form vermiculite. Rossman (1991) interprets the Green Springs to be a flattopped intrusive body with its upper surface approximately coincident with the present land surface. He notes that the pluton contains metasedimentary xenoliths that resemble the enclosing metagraywacke, and has a thermal aureole that is manifested by garnet and biotite porphryoblasts in the surrounding country rocks. Conley and Johnson (1975) concluded that the pluton was rootless at depth on the basis of a gravity study. Vermiculite is being extracted commercially from a deposit near the northeast margin of the pluton.
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.