A vocabulary of landscape — a landscape of words
1190 entries
slickenside
A slickenside is a polished and grooved rock surface produced where two blocks have ground past each other along a fault. The polish can be mirror-bright and the grooves run parallel in the direction of movement, so the surface records exactly which way the fault slipped and, from the small steps along it, which block went which way. It is a fault reading its own history back.
Etymology
The word is an English mining term from at least the seventeenth century, built plainly from slicken, an old form of slick, and side, meaning the wall of a working. Miners met these surfaces constantly because ore often follows faults, and they named the thing long before geology existed as a discipline.
Notes
Reading the sense of movement from a slickenside is one of the standard field skills in structural geology. Running a hand along the surface distinguishes the smooth direction from the rough one, and the rough direction is the way the missing block went. Similar polished surfaces also form in clay soils that swell and shrink, and in landslide shear planes, where they are the evidence that the ground has moved before.