British precious stones miner Gemfields said it had found a 40.23-carat rough ruby at its Montepuez deposit in Mozambique, and termed the find as "one of the most important rubies unearthed in recent times".

The miner said the recent find had been appraised by the Gübelin Gem Lab in Switzerland, ahead of the company's ruby auction in Singapore next month.

"Although difficult to judge in the rough state, the transparency and colour of the crystal indicate an important gemstone might be cut from this piece of rough," said Daniel Nyfeler, managing director of Gübelin.

Rubies are traditionally the most prized when they are a vivid crimson with a hint of blue. However, Mozambican rubies often are a rich pinkish-red colour due to the variation in deposits in the region.

Among the world's most famous rubies are the 100.32 carat Delong Star Ruby and the Hixon Ruby Crystal - a 196.10-carat stone that is touted to be one of the most perfect large ruby crystals in the world.

Earlier this month, an 8.62 carat Burmese ruby was sold at a Sotheby's auction at a record price of about $8.57 million, or almost $1 million per carat.

Gemfields owns a 75 per cent stake in the Montepuez ruby deposit, and in June generated $33.5 million from its first auction of rough ruby and corundum from the deposit.

Gemfields, the world's largest rough emerald producer, has been trying to create a stable market for coloured stones - the same way Anglo American's De Beers has championed diamonds from London's Bond Street to China.

The discovery, which jewellery expert and historian Joanna Hardy termed as "incredibly rare", sent Gemfields' shares up as much as 3.5 per cent on Wednesday. - Reuters