Mined from the mountains of Afghanistan for over six thousand years. Set into Tutankhamun's coffin in ancient Egypt. Ground into pigment by Vermeer in medieval Europe. Traded along the Silk Road at a value equal to gold.

This blue may be one of the first colours humanity agreed to call precious.

A sulphur-bearing composition gives it a depth unlike any other blue stone. The gold flecks across its surface are pyrite—iron crystals laid down over tens of millions of years. Gold scattered through blue. People say it resembles the night sky.