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You are browsing the archive for 2012 May 17.

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 …

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