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| Keywords: Photomicrograph-porphyritic-aphanitic-felsic-rock-USGS.jpg en Photomicrograph of a porphyritic-aphanitic felsic rock Plagioclase phenocrysts white and hornblende phenocryst dark; intergrown with plagioclase are set in a fine matrix of plagioclase laths that show flow structure Plain polarized light; length of photo is 2 6 mm Most felsic rocks are porphyritic with phenocrysts that include plagioclase most common biotite hornblende orthopyroxene rare and orthoclase rare fig 4 Middle Eocene Igneous Rocks in the Valley and Ridge of Virginia and West Virginia 2004 Figure 4 Trip 4 Geology of the National Capital Region ”Field Trip Guidebook Circular 1264 2004 Department of the Interior U S Geological Survey http //pubs usgs gov/circ/2004/1264/html/trip4/fig4 html http //pubs usgs gov/circ/2004/1264/html/trip4/fig4 html United States Geological Survey PD-USGov Uploaded with UploadWizard Granite porphyry samples Microscopic images of crystals | ||||
