Lava column / pillar /Columnar basalt
Lava columns are a feature of basaltic lava flows and form polygonal shaped columns which interlocj. They are formed when a molten basaltic lava flow cools. As the lava cools it shrinks towards a central point and forms polygonal columns of basalt.
The Giants Causeway in N Ireland is extensive area of columnar basalt formed during the rifting which created the North Atlantic Ocean.