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A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. [1]
Fractures are planar or gently curved surfaces of failure produced by brittle failure of rocks. Where the rock masses on either side of a fracture have moved apart slightly, the fracture is called an extension fracture. If the two rock masses have slid past each other, the fractures are shear fractures.
When rocks break in response to stress, the resulting break is called a fracture. If rocks on one side of the break shift relative to rocks on the other side, then the fracture is a fault. If there is no movement of one side relative to the other, and if there are many other fractures with the same orientation, then the fractures are called joints.
Cleavage, fracture, and parting are three related terms that describe how a mineral crystal may break. The orientation and manner of breaking provide important clues about crystal structure and can be keys to mineral identification.
There are four principal classes of fractures: joints, faults (including shears), cleavage, and small irregular breaks. Joints are the prime consideration herein, but other forms of fractures are considered to the extent that genetic, spatial, or transitional relationships exist.
Based on the nature of the displacement discontinuity, commonly encountered fractures can be classified into three geologically based major groups: (1) dilating fractures/joints, (2) shearing fractures/faults, and (3) closing fractures/pressure solution surfaces.
Summarise some basic fracture-related definitions in structural geology. Discuss the basic information needed to solve fracture problems. Define and explain boundary conditions, rock properties, and rock-failure criteria.