Once formed however, these rocks come into contact with water which can cause alteration through a process called hydrothermal metamorphism. The minerals that form in these rocks are stable below the crust, where pressure and temperature is high and there is no water. As the plates moved apart, molten rock rising up from the mantle filled the space created and cooled to form new oceanic floor. The area of what is now Cornwall was at that time a divergent plate margin and new igneous rocks were being created as two oceanic plates moved apart at a spreading ridge.
When the rocks of the Lizard were formed around 400 million years ago, the area was completely submerged by water. The rocks at the Lizard are part of an ophiolite – a piece of oceanic crust that has been uplifted onto continental crust. Kynance Cove, part of the Lizard Complex: © Andy Wright
