In 1996 in the Egyptian Museum in Cairo, Italian mineralogist Vincenzo de Michele spotted an unusual yellow-green gem in the middle of one of Tutankhamun's necklaces.
The jewel was tested and found to be glass, but intriguingly it is older than the earliest Egyptian civilisation.
Working with Egyptian geologist Aly Barakat, they traced its origins to unexplained chunks of glass found scattered in the sand in a remote region of the Sahara Desert.
But the glass is itself a scientific enigma. How did it get to be there and who or what made it?
Horizon: Tutunkhamen's Fireball, made by production company TV6 is on BBC Two at 2100 BST on Thursday, 20 July
