Layered gabbro - Rum
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

Layered gabbro - Rum

This sample of gabbro comes from Loch Uisg on the Isle of Mull, Scotland. It is part of an eroded magma chamber beneath a Paleogene volcano that formed synchronously with basalt lavas on the island. As the volcano magma chamber cooled it formed layering, reflecting processes going on in the chamber that included settling of different mineral phases, influx of fresh magma into the bottom of the chamber, and changing composition of the remaining liquid.

The thin section contains layers rich in olivine and others rich in plagioclase, reflecting the settling and composition changes on short length scales. In this section, the olivine layers appear to display structures with the appearance of sedimentary grading, forming almost 100 per cent of the layer at one point just above a layer of smaller chromite grains (a denser and thus more rapidly settling mineral phase). Plagioclase also forms a cumulate phase intergrown with olivine. Pyroxene is less common and appears to have grown late in the crystallisation sequence, filling spaces remaining between olivine grains.

Additional images
  • layered gabbro (wet) - width 17 cm
  • layered gabbro - width 4 cm
56.3537, -5.8539
Loch Uisg, Isle of Mull, 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
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: