columnar jointing

American  

noun

1. (in basaltic igneous rocks) a series of generally hexagonal columns formed by vertical joints as a result of contraction during cooling.

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Example Sentences

The later basalts are especially marked by columnar jointing, which determines the famous structures of the Giant’s Causeway and the coast near Bengore Head.

From Project Gutenberg

Another characteristic of this group of rocks is the perfection with which many of them show prismatic or columnar jointing, a structure often called "basaltic jointing."

From Project Gutenberg