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7.3.1 Columnar Jointing

Columnar jointing is a special pattern of jointing found in some masses of fine-grained igneous rocks. It consists of sets of cracks produced by the mechanism of cooling. As the rock shrinks with cooling, it contracts about many equally- spaced centers. Polygonal columns are formed having three to eight sides, with six sides being the most common.


Images
Tops of large basalt columns eroded by wave action and glaciation, Irealand
Tops of large basalt columns eroded by wave action and glaciation, Irealand
Original picture from the Ward Collection
A group of basalt columns, Giants Causeway, Ireland  Tops of large basalt columns eroded by wave action and glaciation, Irealand  Devil's Tower, Wyoming.  Columnar joining of basaltic, volcanic plug. Devil's Tower, Wyoming. 

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