If a body of rock is subjected to enough force, it will break and slip along a plane of weakness, the process that we call geological faulting.
Some faults have developed as a result of two tectonic plates moving past each other. These faults are earthquake zones: an example is the San Andreas fault.
Most modern geological structures are the result of past tectonic activity which applies force to the world's rocks.
Finding most types of mineral deposits depends on being able to envisage the structures which lie under the planet's surface.
Geological structures can be economically important. Oil and gas are often found in anticlines or salt domes, and other structures can indicate mineralization.
Some minerals are found near certain geological structures, usually indicating something of the way in which the deposits were formed at some time in the past.
Given suitable pressure and force, apparently solid rocks can fold into complicated structures without breaking. This can happen on a small or large scale.