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Amgueddfa Cymru - National Museum Wales

[image: Slate]

The Slate

What is slate?

Slate is essentially mud that has first been compressed and compacted, and then squeezed and heated by the Earth’s forces. Dinorwig Quarry slates originated as mud deposited in the sea during the Cambrian era of the Lower Paleozoic Age. Movement of tectonic plates formed the mountains of Wales, and provided the pressure to change this mud into slate. The high quality of the slates is a result of the purity of the original mud and sufficient pressure and heat.

Sericite mica, quartz, chlorite, haematite and rutile – these minerals are the main components of slate. Tiny variations in the proportion of some of these minerals can lead to a rainbow of variations in the colours of the slates themselves – from different shades of green through grey and blue to a deep, rich red. Nine layers of slate run through Elidir mountain and they bear such lovely names as: green and wrinkled, redwood, red, old quarry blue, new quarry blue grey, new quarry blue grey mottled, sage green, willow green, bronze, and purple red.

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