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15 May 2012
Diabase dike in diabase
Seen in rip-rap on the side of Naked Creek, a week ago yesterday: This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).