Sawed slab of porphyritic greenstone. Shenandoah National Park, Virginia. No date.

Shenandoah National Park, Virginia. Sawed slab of porphyritic greenstone. Slab is from the outcrop on the south side of Skyline Drive at mile 80.9, about 100 yards east of Big Run Overlook in the southern section of the park. Angular to slightly rounded phenocrysts of plagioclase (now albite) occur in the matrix of finer grained albite, chlorite, and epidote displaying relict basaltic fabric. The phenocrysts in this specimen are somewhat larger than those in the porphyritic flows in the Big Meadows-Stony Man Area, but the texture is typical. Specimen collected by Professor Ernst Cloos, The Johns Hopkins University. Photo by J.P. Owens. Figure 14, U.S. Geological Survey Bulletin 1265.