Garnet Pyroxene Gneiss
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Fact sheet

Garnet Pyroxene Gneiss

This Lewisian rock is from Cleit Thorro, north west of Rodil on South Harris in the Western Isles of Scotland. It was originally a gabbro, intruded in the Archaean period, later metamorphosed in the Laxfordian orogeny when subjected to high temperature and pressure.

In thin section the rock contains large grains of garnet, pyroxene, scapolite, biotite and plagioclase, indicating deep burial and a very high grade of regional metamorphism. The garnet exhibits coronal textures, where rims of minerals reacted with other minerals in the rock as it cooled and decompressed on its journey back to the Earth’s surface following the peak of metamorphism. The rock thus contains evidence of both the prograde path (formed at the peak of metamorphism) and the retrograde path (reactions between minerals as they moved back towards the Earth’s surface).

Additional images
  • garnet pyroxene gneiss - width 4.8 cm
  • Garnet pyroxene gneiss
  • garnet pyroxene gneiss - width 4.8 cm
  • garnet pyroxene gneiss - width 4.8 cm
  • garnet pyroxene gneiss - width 4.8 cm
  • garnet pyroxene gneiss - width 4.8 cm
57.7591, -6.9812
Cleit Thorro, north west of Rodil, South Harris, Western Isles, Scotland
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: