What is Joint (geology)?
[[File:Joints Caithness.JPG|thumb|upright|Joint sets on a plane of [[flagstone]]s, [[Scotland]]]] In [[geology]], a '''joint''' is a [[Fracture (geology)|fracture]] dividing [[Rock (geology)|rock]] into two sections that moved away from each other. A joint does not involve shear [[displacement]], and forms when tensile stress breaches its threshold. In other kinds of fracturing, like in a [[Fault (geology)|fault]], the rock is parted by a visible crack that forms a gap in the rock. Joints push out in various directions, usually [[vertical]]ly. They can have smooth, clean surfaces, or they can be [[Wear (erosion)|scarred]] from sliding against another joint. Joints usually occur as sets, with each set made up of joints that are [[parallel]] to each other.<ref>Engelder, T. & Geiser, P. 1980. [http://www.geosc.psu.edu/~engelder/references/link029.pdf On the use of regional joint sets as trajectories of paleostress fields during development of the Appalachian Plateau], New York. ''Journal of Geophysical Research'', 85, B11, 6319-6341.</ref> Joints become more and more obvious when the rock is [[Weathering|weathered]] (eroded by the elements). When [[water]] gets into the joints, this can lead to the [[Formation (geology)|formation]] of big caves and underground rivers.<ref>{{cite encyclopedia|title=Joint (geology)|encyclopedia=Britannica Online|url=http://www.britannica.com/EBchecked/topic/305597/joint|publisher=Encyclopaedia Britannica|accessdate=15 March 2012}}</ref> ==References== {{reflist}} [[Category:Geology]] {{sci-stub}}