This breccia comes from Trelavour Downs, St Austell, Cornwall. It was transformed from its original granite composition to this brecciated tourmaline-quartz rock by hydraulic pressure and high temperature fluids rich in boron and fluorine that passed through the rock.
In thin section the rock is formed of angular fragments that are veined and broken. One fragment displays fine banding displaced by the brecciation, and another contains larger magmatic tourmaline grains that appear to have been altered. The rock is almost entirely formed of two minerals, tourmaline and quartz.
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.