Garnet epidote skarn
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Fact sheet

Garnet epidote skarn

This rock formed originally as a volcanic ash deposit of andesite composition during the Ordovician period, but was later metamorphosed and transformed by heating and fluids associated with the Shap granite intrusion. It is now best described as a skarn, a term often applied to rocks that have experienced significant heating and strong chemical alteration by granite intrusions. The rock is known in the stone industry as Blue Shap granite, although it is neither blue nor a granite. The term ‘granite’ is used in the stone industry to mean most hard rocks used for building facing or kitchen work surfaces, whereas geologists restrict the use of the term to a specific compositional range of rocks.

Almost half of the thin section is made up of a mosaic of large, pale pink garnet grains growing into one large cavity filled by carbonate minerals, and another cavity filled by quartz. Unusually, this garnet it is not black (isotropic) when viewed between crossed polars but exhibits strong compositional zoning formed when it grew. The finer-grained areas of the thin section exhibit the remains of the volcanic rock texture with some flattened vesicles. Minor amounts of epidote and other accessory minerals are also present.

Additional images
  • skarn - width 18.5 cm (blue spots are paint)
  • skarn - width 23 cm (blue spots are paint)
54.4888, -2.67455
Blue Shap quarry, Cumbria
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: