Joints and fractures
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Joints and fractures are the most abundant signs of strain and deformation in rocks. They are ubiquitous and may part rocks in various regular or irregular sizes as small as a fraction of an inch. The term fracture is general and includes any break in rocks. 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. Fractures caused by weathering, such as exfoliation and spheroidal spalling, are not described.
Jointsare more or less regular groups of fractures paralleled by little or no movement or orientation of rock components. Fractures paralleled by movement are, of course, faults, and those paralleled by considerable or pervasive orientation of minerals or other rock components are cleavage of one sort or another. Small, irregular, and inconsistently oriented...
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