Aegirine granite - Rockall
Click the microscope button to view a thin section for this sample.
Click the microscope button to view a thin section for this sample.

Fact sheet

Aegirine granite - Rockall

This sample of granite is from the island of Rockall, which lies almost 600 km west of the Scottish mainland and is thus the most westerly rock in the UKVM collection. It is included in the UKVM collection because Rockall is recognised as part of the UK by the United Nations, although ownership is disputed and the island is also claimed by Iceland, Denmark (via the Faroe Islands) and Ireland. The island's importance lies in its remote location, and claims concerning fishing rights and ownership of the oil-rich continental shelf. The granite island is the tip of a much larger volcanic edifice that erupted during the Paleogene and is part of the large North Atlantic volcanic province that stretches from Greenland to southern England.

The thin section shows this to be a coarse-grained granite rich in aegirine, a sodium-rich pyroxene with unusual patchy green colouring and pleochroism ranging from green to straw-yellow. The feldspar shows evidence of extensive exsolution to orthoclase and plagioclase, and is mottled when viewed in plane polarised light. The quartz grains appear clear and undeformed. The rock is known to contain several unusual secondary minerals including bazirite, elpidite, leucophosphite and apatite, although they are not prominent in this thin section.

Additional images
  • Three crystals of bazirite on riebeckite - width 700 microns
57.5967, -13.0553
Rockall, North Atlantic
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
Accessory minerals
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: