DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
En echelon veins are parallel oriented structural features in rocks that result from shear forces. They appear as sets of stepwise overlapping lenses within the rock and originate as tension fractures that run parallel to the major stress orientation in a shear zone. The fractures are subsequently filled by precipitation of a mineral, most often quartz or calcite. As soon as they form, they begin to rotate in the shear zone. En echelon veins may help geologists to analyse the deformation history of the rock.
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