Blindfolded on a camel

Ripert said that he had been guided — blindfolded — by a local chieftain to a natural source of iron 12 hours' camel ride to the south-east of Chinguetti. He bagged a 4 kilogram (8.8 lb) fragment of the rock, which found its way to Paris some years later, where geologist Alfred Lacroix pronounced it to be an important discovery (see Lacroix Report). But despite the attempts of several expeditions since then, no one has managed to locate the outcrop it allegedly came from. So was the whole story a hoax?

French fossil expert Professor Théodore Monod spent decades searching but concluded that Ripert was mistaken. Now, armed with a magnetometer (which detects tiny changes in the Earth's magnetic field) and Ripert's descriptions, meteoricists Sara Russell and Phil Bland travel to Chinguetti in the hope that they will succeed where Monod and others failed. Once there, they join Bob Watt, a Metropolitan Police sergeant who is a bit of an Indiana Jones in his spare time, having led several previous desert expeditions.

A great stone from the sky

First, Bland checks the ancient local walls for iron nails to see if their origin could be meteoritic — Ripert's original interest had been prompted by the use of iron utensils in the area. But the result proves negative. Then the team hears of a second black rock in the desert that could be a meteorite. Unfortunately, what the scientists find, after a two-day camel trek, are small lumps of sandstone.

As the British party begin to wonder if they're being duped, the town's imam tells them that he has heard talk of a great stone that fell from the sky, although he doesn't know whether it exists.

The explorers continue their quest, along the way visiting the Aouelloul impact crater, an unrelated, less controversial meteoritic site that was first discovered from the air in 1938 by an explorer called Pourquié. Then they find the rocky hill that Monod thinks is the one Ripert described, but instead of a shining mass with metallic spikes on top, as Ripert claimed, the expedition is faced with yet another sandstone red herring.

Shifting sands

Back in the Mauritanian capital, Nouakchott, the trio's spirits are lifted when they meet Jacques Gallouédec, who worked for many years for the Mauritanian water board. He claims to have seen the meteorite in the 1980s from the air and provides drawings and map references. The scientists are eager to get looking and, on the way, cheer up when they discover bits of magnetite that could be — but aren't necessarily — chips from a meteorite. But when they eventually reach the area indicated by Gallouédec, the readings from their magnetometer (which can detect the presence of iron) are not encouraging. Perhaps the shifting sands have buried the great rock.

In the end, they decide to have the Chinguetti fragment, now lodged in Paris, tested at the University of California to see if it could have come from a much larger mass. If it did, at least they'll know that the rock is out there somewhere. But if it didn't, how did such a seemingly trustworthy man as Ripert get it so wrong?