Vertical cracks/fractures that are created without displacement
Occur in most rocks, often in regular patterns
In igneous rocks, cooling joints form when magma contracts as it loses heat
In sedimentary rocks, they form when rock is subject to compression or stretching by tectonic forces
When overlying rock is removed, underlying strata expand and stretch, crating unloading joints parallel to the surface
Increases erosion rates by creating fissures which marine processes can exploit