What does the term 'rigidity' refer to in the context of geological stress?

In the context of geological stress, rigidity refers to the ratio of shearing stress to angular rotation in a rock sample. This concept highlights how resistant a rock or material is to deformation under applied forces. Rigidity is a key factor in understanding how rocks respond to tectonic forces, which helps in predicting behaviors like faulting and folding in the Earth's crust.

This property is crucial because a more rigid material will undergo less deformation compared to a more ductile material when subjected to the same stress. Therefore, when stress is applied, the ability of the material to resist that stress and maintain its shape—characterized by rigidity—plays a vital role in assessing geological stability and the mechanics of rock masses.