Nasii

Columnar  Basalt

When  a thick lava flow cools, it contracts vertically
but cracks  perpendicular to its directional flow with remarkable geometric  regularity
- in most cases forming a regular grid of remarkable  hexagonal extrusions
that almost appear to be made by man.  

One  of the most famous such examples is
the Giant’s Causeway on the coast  of Ireland (shown above),
though the largest and most widely recognized  
would be Devil’s Tower in Wyoming .

Basalt  also forms different but equally fascinating ways
when eruptions are  exposed to air or water.