Explosion breccia - Wheal Remfry
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Fact sheet

Explosion breccia - Wheal Remfry

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.

Additional images
  • explosion breccia - width 16 cm
  • Angular host rock fragments in glass matrix – 28 cm
50.3816, -4.9214
Wheal Remfry china clay pit, St Austell, Cornwall
About this collection

The United Kingdom Virtual Microscope (UKVM) collection consists of igneous, sedimentary and metamorphic rocks from around the UK.

It is intended as a teaching resource, helping to tell the story of the common rock types and how they form, and reflecting the history of the UK at the margins of the continent of Europe. The collection is a series of teaching sets, for example igneous rocks from the North Atlantic Igneous Province and SW England; high-temperature metamorphic rocks from Scotland and low-temperature metamorphic rocks from Wales; and sedimentary rocks, including English limestones and sandstones.

Sample details

Rock-forming mineral
Category guide  
Category Guide
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow users to search for broad terms like ‘granite’ as well as more specific names such as ‘breccia’. However, the adjacent descriptions of the specimens captures a wider range of general words and phrases and is a more powerful search tool.
Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Selecting one or more period, for example 'Jurassic'.
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
The owner of the sample that appears in the collection. For example, NASA owns all the samples that appear in the Moon Rocks collection
We would like to thank the following for the use of this sample: