2009
SN1333 : Contraction joints in rhyolite
taken 16 years ago, 3 km from Eglwyswen, Pembrokeshire/Sir Benfro, Wales

Contraction joints in rhyolite
After eruption, these igneous rocks - rhyolite here at Carn Alw, dolerite elsewhere in the area - cracked during cooling along straight lines and often subsequently split into blocky, angular shapes.