Harpers formation subgraywacke

Harpers formation subgraywacke, Rockbridge County, VA. Typical section. Most of the grains in shades of gray are quartz, except for the large fractured grain at right and the dark oblong grain at lower left, both of which are feldspar. The high-birefringence grains are phyllosilicates - mostly muscovite and a little chlorite. Photomicrograph in XPL. Imaged area 0.56 mm by 0.83 mm.