The world’s largest polished, solid-form black opal could be yours if you have a spare million dollars.

“The Pacific”, a gargantuan opal found near Lightning Ridge in New South Wales, is being sold at auction this month by Noble Numismatics.

Unearthed in 1989 by opal miner Gerald O’Brien, it was named after the world’s biggest ocean because of its size and its vivid, iridescent blue colours.

The opal weighs 443.56 carats, or around 90 grams.

It was listed as the world’s largest black opal – considered the rarest form of the gemstone – in the 1990 Guinness Book of World Records.

The auction house describes the sale, for the first time since its discovery, as “a once in a lifetime opportunity to own an Australian mineral specimen icon”.

Noble Numismatics has valued the opal at $700,000, which does not include a 22 per cent buyers premium.

But for that price, the seller is throwing in a copy of the 1990 Guinness Book of World Records, which lists The Pacific.

The Pacific was unearthed in 1989 by opal miner Gerald O’Brien in Lightning Ridge. Photo: AAP

The black opal is one of hundreds of lots up for grabs in the auction, which begins on November 24 at the State Library of NSW.

Also up for sale is some of Australia’s first locally-produced legal tender, dating back to 1813, 19th-century gold sovereigns, and a large collection of Greek, Roman and Byzantine coins dating back to 350 BC.

-AAP