Riebeckite microgranite
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Fact sheet
Description: 

The Isle of Ailsa Craig lies in the Firth of Clyde, Scotland. It is the plug of an ancient volcano, formed during the Paleogene period during the eruption of the North Atlantic volcanic province. Ailsa Craig is composed almost entirely of one rock type: a homogeneous fine-grained microgranite that has made Ailsa Craig famous as a source of curling stones. The stones from this island came to prominence in the early 1800s when it was recognised that the very hard, fine-grained microgranite has a texture that resists fracture and water absorption, making it ideal for curling stones.

In thin section the sample is very fine-grained for a rock characterised as a granite. The thin section contains small grains of riebeckite (a blue-green amphibole) and arfvedsonite (a blue-green amphibole). Both minerals are abundant and visible in the thin section but the grains are too small to allow the user to recognise the key discriminating indicator of cleavage angle. The rock also contains quartz, plagioclase and orthoclase feldspar.

In Place
In Time
infoImage: 
Location description: 
Ailsa Craig, Firth of Clyde, Scotland
Accuracy:
Location precision: 
Moderate
Timescale:
Timescale: 
Paleogene
Ma = Millions of years ago
In Focus
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Type:
Type: 
igneous
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