Pink to gray, coarse-grained, massive, strongly-lineated gneiss ranging in composition from granite to quartz monzonite (Henika, 1977), composed of microcline and perthite augen enclosed by biotite in a quartz-plagioclase matrix. A characteristic linear fabric is produced by rod-like feldspar porphyroblasts and crystalline aggregates. Thin veins of purple fluorite are common. Mineralogy: quartz + potassium feldspar + plagioclase + biotite + muscovite ± pyrite ± fluorite. Geophysical signature: pronounced positive radiometric signature, flat magnetic signature. Originally named Shelton granite (Jonas, 1928), the unit was renamed Shelton Formation (Henika, 1977). Simple linear fabric was cited as evidence for an intrusive origin by Henika (1980). The Shelton has been dated at 424±7 Ma (Rb-Sr whole-rock; Kish, 1983) and 463 Ma (U-Pb; Hund, 1987).
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.