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Granite

granite rock sample

Granite forms the backbone of Cornwall stretching from Dartmoor in Devon South-westwards to the Isles of Scilly.

Granite and its associated minerals have underpinned the Cornish economy for hundreds of years.

Igneous rocks like Granite were once molten and forced their way into and under rocks by their natural buoyancy. Granite rocks form deep underground as giant batholiths, which can be tens or even thousands of kilometres across. Even though granite forms deep underground, it is often seen on the surface because it has such a high quartz content which makes them really tough! This means that Granite rock can survive long after softer rocks around them have eroded away.

Granite is a light coloured, speckled rock and is very ‘acidic’ – it has high silica content,  in the form of quartz. They also contain soft black flakes of mica. The large crystals, feldspar, visible in Cornish granite indicate that it formed by cooling slowly deep underground, and then exposed by erosion of other surrounding rock.

Hard Fact:

The granite batholith under Cornwall is estimated to be 68,000 cubic kilometres!

Richard Garnett: Geevor Geologist (1960-1973) wrote a 253 page book just about the ‘Lands End Granite’

View this mineral in 3D

 

Photograph reproduced with the kind permission of the Geevor Archive

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