Joint (geology)
In geology, a joint is a fracture dividing 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, the rock is parted by a visible crack that forms a gap in the rock.
Joints push out in various directions, usually vertically. They can have smooth, clean surfaces, or they can be scarred from sliding against another joint. Joints usually occur as sets, with each set made up of joints that are parallel to each other.[1]
Joints become more and more obvious when the rock is weathered (eroded by the elements). When water gets into the joints, this can lead to the formation of big caves and underground rivers.[2]
Joint (geology) Media
Horizontal joints in the sedimentary rocks of the foreground and a more varied set of joints in the granitic rocks in the background. Image from the Kazakh Uplands in Balkhash District, Kazakhstan.
Joints in the Almo Pluton, City of Rocks National Reserve, Idaho.
Columnar jointed basalt in Turkey
Columnar jointing in basalt, Marte Vallis, Mars
Recent tectonic joint intersects older exfoliation joints in granite gneiss, Lizard Rock, Parra Wirra, South Australia.
Roadside weathered diorite outcrop along the Baguio-Bua-Itogon Road in the Philippines showing joints.
Plumose structure on a fracture surface in sandstone, Arizona
References
- ↑ Engelder, T. & Geiser, P. 1980. 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.
- ↑ "Joint (geology)". Britannica Online. Encyclopaedia Britannica. Retrieved on 15 March 2012.
