Cracking the code of hexagonal rocks (aka columnar jointing)

Also, studies into fracture mechanics (the way a crack releases the built-up tension in the material) found that the stress in the contracting rock is most efficiently relieved by three fractures meeting at 120 degree angles. So while the initial cracks are all over the place, they eventually settle into the path of least resistance - hexagons. Why Hexagonal Basalt Columns? by M Hofmann, R Anderssohn, H-A Bahr, H-J Weiss, and J Nellesen (2015)