Explosion breccia - Wheal Remfry
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Fact sheet
Description: 

Wheal Remfry is a working china clay pit in the St Austell granite complex. It hosts the spectacular hydrothermal explosion breccia. Hydrothermal breccia formed in a granitic magma chamber when there was a build-up and sudden release of pressure below an earlier crystallised granite roof. Boron-rich fluids accumulated as the magma crystallised, and when the pressure of these fluids exceeded the weight of the rock above (known as the lithostatic load) the fluid escaped catastrophically through vertical fractures. On reaching the surface the pressure suddenly dropped, leading to explosive decompression and break-up of the surrounding rock. The breccia contains granite and mineral fragments in a mainly quartz-tourmaline-rich matrix (the black material). The specimen also shows a large reddened orthoclase-feldspar-rich microgranite fragment and a piece of the altered granite wall rock. The specimen was collected by Andy Tindle (The Open University) with the help of Jeremy Hooper of Imerys Minerals Ltd, Par, Cornwall.

In Place
In Time
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Location description: 
Wheal Remfry china clay pit, St Austell, Cornwall
Accuracy:
Location precision: 
Good
Timescale:
Timescale: 
Permian
Ma = Millions of years ago
In Focus
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Type:
Type: 
igneous
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