A $300,000 award offered for 162.5-ct. diamond

An unfinished pink diamond, described by experts as ‘unbelievably pure and extremely rare,’ has disappeared on its way from Geneva to South Africa, according to a report Thursday on ABCnews.com.

A $300,000 reward is being offered for the 162.5-ct. gemstone, in hopes that the whole world will be on alert for the stone-and the thieves will be unable to sell it, ABC reported.

The Swiss daily Blick carried an advertisement for the reward, along with two phone numbers, but it was unclear who was offering it, ABC reported.

The raw diamond was being transported from Geneva to Zurich on Jan. 23, reported Blick. The stoneshould have been on an airplane headed to Johannesburg-but it never arrived.

Professionals from the Swiss arm of the security firm Brinks had guarded the stone.

The report said there was a deep mystery around the 32.5-gram (1.146-ounce) stone: No pictures have been taken of it, and no one knows where it was discovered.

Pink diamonds are among the most rare and precious of diamonds, and are primarily found in Australia.

It was also unclear who owned the diamond or why it was on its way to South Africa.

Once the diamond is polished it could be worth $12 million, Blick reported, but its true price could only be determined at auction.

British insurance company Lloyd’s of London contracted a specialty firm to investigate the case, according to Blick. It quoted Cristoph Berguet, a purported diamond hunter, as saying he hoped the reward and increased attention would lead to the thieves.

But Lloyd’s of London told Reuters it had not offered the reward or sent any special teams to Switzerland for the case.

”Lloyd’s is not the sole insurer of the gem, but is one of several insurers who have provided cover,” the insurer said in a statement.