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.
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.