$6m raw diamond goes missing

The stolen diamond is uncut, like the Giant Sefadu (above)

A reward is being offered after an "extremely rare" diamond disappeared en route from Geneva to South Africa.

The insurers Lloyds of London is offering 500,000 Swiss francs ($303,000) for the return of the raw diamond, worth at least 10 million Swiss francs ($6m).

Once cut the value of the 162.4 carat pink stone could double.

It was known to have arrived safely in Zurich on 23 January and was transferred to a flight bound for Johannesburg.

We can be happy that nobody died

Security official

But it never arrived.

The diamond is "of unbelievable purity and extremely rare" according to an expert quoted by German-language Swiss newspaper Blick.

It was a "terrible loss" an official at Brinks security firm told the tabloid.

But "we can be happy that nobody died" he added.

Mystery owner

There is no picture of the diamond and its origin is not known. However, according to Blick the majority of pink diamonds come from Australia.

South African police are leading the investigation with the co-operation of officers in Zurich.

Police have not named the owner or recipient of the jewel.

Lloyd's detectives are also investigating.