Garnet epidote skarn
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Fact sheet
Description: 

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.

In Place
In Time
infoImage: 
Location description: 
Blue Shap quarry, Cumbria
Accuracy:
Location precision: 
Good
Timescale:
Not known
Ma = Millions of years ago
In Focus
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Type:
Type: 
metamorphic
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