Fault surfaces have many structures associated with them. Commonly the fault surface can be grooved - rather like a glaciated pavement. This analogue is highly pertinent because glacier ice can be considered in some ways to be a rock (a solid earth material) which, in flowing across the bedrock, abraids the surface. And the striations and grooves on fault surfaces can have the same significance - they document the direction of relative fault motion!
Fault surfaces can also open up small voids into which new minerals can be precipitated (click here to see an example). If precipitation keeps up with the rate of fault slip then the new mineral can be fibrous. The imprecise term for these features is slickenside. A better term is shear fibre. The long directions of the fibres tell you about the relsative slip direction of the fault and the sense of fibre growth off the fault wall rocks can give you the sense of faulting - just like a pull-apart basin on a strike-slip fault (you can link to strike-slip faults or to the general pages on faults by clicking here but beware losing navigational control in these websites).
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