Stress causes rocks to deform, meaning the rocks change size or shape. There are different kinds of stress that rocks experience, and these determine how the rocks deform. Tensional stress is when rock is stretched apart. Compressional stress is when rock is pressed together.
In this way, what is brittle deformation?
Generally, rocks respond to stress in one of two ways: they break, or they bend. When a rock breaks, it is called brittle deformation. Any material that breaks into pieces exhibits brittle behavior. When rocks bend or flow, like clay, it is called ductile deformation.
Why do rocks deform?
When rocks deform in a ductile manner, instead of fracturing to form faults or joints, they may bend or fold, and the resulting structures are called folds. Because the strain rate is low and/or the temperature is high, rocks that we normally consider brittle can behave in a ductile manner resulting in such folds.
How are stress and strain defined as they apply to rocks?
Strain is a change in shape or size resulting from applied forces (deformation). Rocks only strain when placed under stress. Ductile deformation is also called plastic deformation. Structures in geology are deformation features that result from permanent (brittle or ductile) strain.