HYDROTHERMAL BRECCIA - 2.5 billion years old - South Africa

Hydrothermal breccias are formed by the fracturing of rocks deep underground by hot water under extremely high pressure. Reduction in pressure causes the water to boil and the result is a churning mixture of rock, steam and boiling water.

These ‘hydrothermal fluids’ carry dissolved chemicals which crystallise in the fissures to form minerals which cement the fragments into a solid rock called a breccia.

This attractive and colourful rock consists of fragments of iron-rich chert cemented by quartz.