Marble - Donegal
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Fact sheet
Description: 

This rock sample was originally a limestone deposited in the Proterozoic era. It metamorphosed to a marble during the Grampian orogeny around 480 million years ago but crystallised very few of the metamorphic indicator minerals that George Barrow (1853—1932) used when he defined ‘Barrovian metamorphic zones' (chlorite-biotite-garnet-staurolite-kyanite-sillimanite) in the Scottish Highlands. The sample comes from south east of Lough Finn, County Donegal, Ireland in a series of rocks that are correlated with the Scottish Dalradian. 

The thin section is dominated by calcite, with quartz grains that form patches of both silty lithologies and individual grains in a calcite matrix. Deformed muscovite in the silica-rich areas may be original sedimentary grains and, if so, their presence indicates low grade metamorphism, possibly as low as chlorite or biotite grade.

In Place
In Time
infoImage: 
Location description: 
Lough Finn, Co. Donegal, Ireland
Accuracy:
Location precision: 
Poor
Timescale:
Timescale: 
Cambrian
Ma = Millions of years ago
In Focus
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Type:
Type: 
metamorphic
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