SLICKENSIDES - Egremont, Cumbria

A slickenside is a smoothly polished surface caused by frictional movement between rocks along a fault. This surface is usually striated in the direction of movement and therefore helps with our understanding of earthquake propagation.

The rapid grinding between two rock surfaces deep underground reduces the particle size so dramatically that the surface becomes shiny. However, the precise mechanisms that creates slickensides is not well understood.

This is a superb example in hematite rock, with a lustrous grinding surface.