//Carboniferous Millstone Grit

Carboniferous Millstone Grit

Around 325 million years ago a chain of mountain range stretched from mid Wales to Belgium. The rivers flowing from the mountains swept loads of sediment towards the sea.

The first of sediments to accumulate along the shores were banks of pebbles and then, later, sand banks.

The mixture of pebbles and sand gave rise to conglomerate rock known as Millstone Grit, and the small white boulders in this flower bed are examples of this rock.

Tough and sparkling

This conglomerate rock is visually distinctive as it is full of large white rounded pebbles of quartz and sand grains. Quartz is very hard, to the degree that crystals and fragments can be continually re-cycled.

Pure as steel

The silica in the quartz is so pure that it can withstand very high temperatures. As a result, the Millstone Grit was quarried on a large scale in south Wales to help make furnace windows and fire bricks for the south Wales steel industry.

origin of  the Carboniferous Millstone Grit sampleWhere do these rocks come from?
Carmel Quarry, Carmarthenshire


Carboniferous Millstone Grit display at the NBG

Port Talbot steelworks at night
Port Talbot steelworks at night

A steel-making blast furnace
A steel-making blast furnace

quartz crystal
A quartz crystal