The bluestones at Stonehenge are the smaller rocks you can see standing inside the huge sarsens that form the outer circle and the inner trilithons.

They range in size from stumps barely visible in the turf through to slender pillars standing nearly 2.5m tall (plus another metre or more below gound) with the largest weighing between 2 and 3 tonnes.

These rocks definitely come from the Preseli Mountains in southwest Wales, 150 miles from Stonehenge as the crow flies. Their place of origin was first established in 1923 by the geologist H. H. Thomas and has been confirmed by modern geochemical analysis. They used to be known as the “foreign stones” because it was recognised that they weren’t local to the Stonehenge area.

The name bluestone is a collective term and there are two main types – spotted dolerite and rhyolite.

It’s not obvious why they’re called bluestones to most…