Ripert said that he had been guided blindfolded by a local chieftain to a natural source of iron, after a 12-hour-long camel ride to the south-east of Chinguetti.

He bagged a 4-kilogram fragment of the rock, which found its way to Paris some years later, where geologist Alfred Lacroix pronounced that it was an important discovery.

Ripert wrote to Professor Théodore Monod in 1934: 'I know that the general opinion is that the stone does not exist; that to some, I am purely and simply an impostor who picked up a metallic specimen.

Despite various searches over the years, Monod concluded in 1989 that Ripert had been mistaken: 'An error was made in the identification of the rock of a 40-metre hill that is entirely sedimentary with no trace of metal,' he wrote.

In 1980, former French air force officer Jacques Gallouédec was carrying out aerial surveys for the Mauritanian water authority, when he spotted a strange semi-circular ground formation to the south-east of Chinguetti.