Definition of columnar jointing
Parallel, prismatic columns, polygonal in cross section, in basaltic flows and sometimes in other extrusive and intrusive rocks. It is formed as the result of contraction during cooling.
Discussed on Mindat, with many additional images, https://www.mindat.org/mesg-630094.html.
Synonym of: columnar structure
Ref: AGI
Changes in cooling rates result in differences in size of the columns. The upper flow would have cooled more slowly.
Discussed on Mindat, with many additional images, https://www.mindat.org/mesg-630094.html.
Synonym of: columnar structure
Ref: AGI