Joint (geology)

A joint is a fracture in rock along which there has been little or no displacement. Joints divide rock into blocks and can guide weathering, fluid flow, and slope failure.

Fracture mechanics: The study of how cracks initiate, grow, and interact in materials. Explains how stress and rock properties control joint initiation and growth.
Fault (geology): A fracture or zone of fractures in rock along which measurable displacement has occurred. The defining distinction is that faults accommodate displacement, unlike joints.
Hydrogeology: The study of groundwater occurrence, movement, and properties. Joints can dominate groundwater flow through otherwise impermeable rock.
Columnar basalt: Basalt divided into polygonal columns by contraction fractures formed during cooling. Its columns are bounded by joints produced as lava cooled and shrank.
Tensile stress: Stress that pulls material apart across a plane. Joints commonly open when tension exceeds the rock’s tensile strength.
Fracture (geology): A break in rock that may or may not involve displacement. Joints are one kind of fracture, distinguished by negligible displacement.
Fractured aquifer: An aquifer in which groundwater flows chiefly through fractures in rock. Open and connected joints can supply its principal flow paths.
Devil's Postpile National Monument: A California monument preserving a striking exposure of columnar basalt. Its columns make cooling joints visible at landscape scale.
Mode I fracture: A crack-growth mode in which tensile loading opens the crack faces apart. Many joints form by this opening mode, with little shear displacement.
Vein (geology): A mineral-filled fracture or fissure in rock. Minerals can precipitate in joints as fluids move through them.

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