Cordierite/mullite nodule in basalt
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Fact sheet

Cordierite/mullite nodule in basalt

This xenolith sample comes from Kilfinichen Bay, Isle of Mull, Scotland, where it was discovered in basalt intruded during the Paleogene. The rock was originally a sediment metamorphosed during regional metamorphism in the Caledonian orogeny, but was then subjected to very high temperatures (up to 1100 °C) as it became incorporated in the lava flow during the Paleogene period. This rock is an extreme version of contact metamorphism leading to complete recrystallisation of the original minerals in the rock and even the formation of pockets of melt.

Melt pockets that formed during immersion in the basalt lava flow are prominent in the thin section, and are formed of a randomly oriented matrix of fine-grained plagioclase and pyroxene. Vesicles in the melt pockets have been filled by zeolites with radiating crystal bundles. Large grains of cordierite (unusually free of mineral inclusions) exhibit sector zoning, and circa 100 micron grains of cordierite dominate many of the remaining areas of the thin section. The rare mineral mullite is present, visible in this thin section as radiating stars of lozenge-shaped crystals and easily recognised by its pink colour and pleochroism. 

Additional images
56.3819, -6.0708
Kilfinichen Bay, 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
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).
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We would like to thank the following for the use of this sample: