This fine-grained porphyritic igneous rock comes from Wolf Rock, a tiny part of land that lies in the treacherous waters between the Isles of Scilly and Land's End. This island off the coast of Cornwall is best known for its granite lighthouse, built between 1861 and 1869, which covers most of the area above water. The phonolite was intruded around 130 million years ago and is one of a suite of alkaline intrusions of similar age.
The thin section illustrates the fine-grained igneous of groundmass of sanidine, nepheline and augite pyroxene. Phenocrysts are dominated by tablular sanidine, although there are rounded, embayed and sometimes altered nepheline phenocrysts also present (see rotation 1). Dark brown six sided euhedral nosean phenocrysts are also present and contain abundant inclusions. In places the nosean phenocrysts are partially altered to analcime.
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.