Basaltic andesite with cordierite nodule
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

Basaltic andesite with cordierite nodule

This sample is a xenolith from the upper part of a sill sheet in the Loch Scridain Sill Complex on the Isle of Mull, Scotland. The Scridian Complex is intruded into Moine (Neoproterozoic) crystalline basement rocks beneath the Mull central volcano. It consists of a series of high-level, inclined, xenolithic sheets, ranging in composition from basalt, through andesite and dacite, to rhyolite. This sample is an unusual composition xenolith in a basaltic andesite sill.

In thin section the xenolith is dominated by large cordierite crystals that appear to have back reacted with the liquid magma. The cordierite is relatively inclusion-free although brown-stained adjacent to the liquid, and exhibits characteristic strong polysynthetic twinning. The basaltic andesite is fine-grained and appears to have invaded the xenolith while liquid. Away from the xenolith the plagioclase crystals are randomly oriented, but between the cordierites the crystallisation appears to vary, often forming radiating bundles.

Additional images
  • cordierite nodule - width 5 cm
56.3372, -6.1503
Loch Scridain, 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
Category guide  
Category Guide
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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
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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).
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We would like to thank the following for the use of this sample: