British entrepreneur and philanthropist Max Ostro ventured deep into the wilds of the Amazon jungle 30 years ago and returned with something very special.

What the real-life Indiana Jones found was a flawless blue topaz gemstone, said to be the largest of its kind.

Next month, the Ostro stone (left) will go on display at London's Natural History Museum, according to a Reuters report.

The gemstone weighs about 2kg and will be exhibited from Oct 19. It is on permanent loan to the museum said, the report added.

Its value was not disclosed.

Mr Ostro, who died in 2010 at age 84, found the gemstone in Minas Gerais, in south-eastern Brazil.

The Ostro stone is the largest cut topaz to go on show at the museum. It is an impressive 9,381 carats and will be displayed alongside specimens from one of the world's most important mineral collections, the report said.

Experts said there has never been a piece of blue topaz of this "intensity and quality", reported British news website BT.

Extra security will be in force to protect the deep blue gem, which will be kept in a 2m-high toughened glass case, the report said.