  Outcrops of columnar joints made of solidified lava flows are often covered
by semi-ordered polygonal cracks. The polygon diameters are fairly uniform at
each outcrop, but their shapes largely vary in the number of sides and internal
angles. Herein, we unveil that the statistical variation in the polygon shape
follows an extreme value distribution class: the Gumbel distribution. The
Gumbel law was found to hold for different columnar joints, regardless of the
locality, lithologic composition, and typical diameter. A common distribution
for columnar joints implies a new universal class that may integrate the
polygonal crack networks observed on the surface of various fractured brittle
materials.
