You are browsing the archive for 17 May 2012 - Mountain Beltway.
17 May 2012
More percussion marks
Yesterday, I introduced percussion marks to this blog space. Here are some other shots of this distinctive “shatter” structure, but in a vein of hydrothermal (milky) quartz exposed on Bear Island, between the C&O Canal and the Potomac River (about right here, just west of the trail): Sometimes percussion marks are accompanied by radial fracture sets like this one… I interpret these radial fractures (sometimes with small cone-fractures at the …