Visitors to South Australia from 25 September will have the chance to go back in time 100 million years to a time when dinosaurs roamed Australia, the southern desert was a huge inland sea populated by huge Mesozoic monsters and some of the world's most wondrous gemstones began being formed.

Opals, a multimillion dollar exhibition by the South Australian Museum will be a once-in-a-lifetime chance to see some of the rarest, most beautiful and spectacular opals ever discovered in Australia.

The exhibition's star attraction is the Virgin Rainbow, described by museum director Brian Oldman as 'the most wondrous and unique opal yet discovered'.

Also on display will be an opalised skeleton of one of the aforementioned monsters – a 6.5m plesiosaur – which died as the inland sea dried up.

The creature – the marine reptile equivalent of a dinosaur – is named the Addyman Plesiosaur, after its finders.

Ancient climate change

The Addyman Plesiosaur was opalised when water and silica hardened in its bones over millions of years.

Meanwhile the South Australian desert became a desolate moonscape above the plesiosaur's forgotten carcass thanks to climate change in the Cretacious, around 100 million years ago.

It was found by a husband and wife pair of amateur prospectors in 1968 on almost their first day on the job.

But back to the centrepiece of the exhibition, the 6cm long Virgin Rainbow, which is worth over $1 million and is on display for the first time to celebrate the 100th anniversary of the beginning of opal mining in Australia.

"If you take the Virgin Rainbow – it's almost as if there were a fire burning in there because the movement and the colour changes are constant," Oldman said.

"It is perpetually different – not just if it's under different light or the way you hold it, but because of the way the shapes inside refract the light."

It is believed the Virgin Rainbow formed from the pocket left by the bone of a dead belemnite – a long extinct form of squid that possessed an internal skeleton.

The gemstone, which seems to breathe a multi-hued fire of reds, gold, greens and black, was discovered in Coober Pedy by opal miners John Dunstan, Tania Burke and Dale Price in 2003.

"You'll never see another piece like that one, it's so special. That opal actually glows in the dark — the darker the light, the more colour comes out of it, it's unbelievable," Dunstan told the ABC recently.

"I've done a lot of cutting and polishing. I've been doing it for 50 years, but when you compare it to the other pieces that claim to be the best ever, this one just killed it."

A tribute to the miners

In addition to the amazing sights, visitors will be able to take in the smells of an authentic Coober Pedy opal mine and an immersive display that explores the science of opals.

"We gathered earth from Coober Pedy and put it in a mine that we recreated from a mould of an actual working mine as part of the exhibition," said Oldman.

"So you even get the smell of what it was like to be a miner – we have created an immersive experience.

"It's a tribute to the ingenuity and dedication of the miners who gave their labour and even their lives so that we can admire these amazing gems."

Oldman said the exhibition has quite literally been 100 million years in the making.

"That is how long it took opals to form, from when dinosaurs walked the Earth and central Australia was an inland sea."

The museum has also gathered some of the most unique and fascinating opals from around the world to complement its own collection and showcase the beauty and diversity of Australia's national gemstone.

"From jewellery to fossils, to specimens embedded in rock, visitors will be treated to a spectacle of unmatched colour and beauty," said Oldman.

"A range of activities will be on offer throughout the exhibition to allow visitors to delve into the geology and history of opals and discover the science behind their signature play of colours.

"It will have a rich South Australian flavour, which is unsurprising given that 90 per cent of the world's opals come from this state," he said.

Finest gems gathered from around the globe

Oldman said the international collection is a testament to the strength of the museum's global networks.

"It will feature a collection of a quality never before seen in one place – this is a once-in-a-lifetime opportunity."

"It is quite simply the finest collection of opals ever assembled in one place and it's unlikely that this collection of opals will ever be seen again.

"It tells the whole story of opals, from how they formed, the tenacity of the miners all the way through to the creation of opal jewellery."

The first opal was discovered in 1914, when a boy named Willie Hutchison went on a gold mining expedition with his father.

"The story goes that Willie set out in search for water one day, rather than staying at camp as he'd been instructed to do by his father."

"He came back to camp with water, but also with precious opal gemstones."

Over time this led to the creation of opal mining communities in places like Coober Pedy, Andamooka and Mintabie, which have remained opal mining hubs to this day.

"It is ironic that in the most harsh of terrains the most beautiful of naturally occurring gems are now found."

Proof of water on Mars

When the inland sea dried, acid levels in the top sandstone deposit were boosted, releasing silica that would later seep into the pockets left by the bones of long-dead plesiosaurs.

Later as acid levels rose the silica hardened into opals. No other environment in the world is known to have undergone this same process.

Interestingly, just as the presence of opal reveals inland Australia's aquatic past, the discovery of opals on Mars confirmed the existence of water there long ago and expanded the timeframe when water existed on the Red Planet.

The NASA discovery back in 2008 suggested that liquid water remained on the planet's surface a billion years later than scientists believed, and it played an important role in shaping the planet's surface and possibly hosting life.

Researchers examining data from the orbiter's Compact Reconnaissance Imaging Spectrometer for Mars found evidence of hydrated silica, commonly known as opal. The hydrated, or water-containing, mineral deposits are telltale signs of where and when water was present on ancient Mars.

A humbling experience

Oldman said he is humbled to have played a part in the show.

"It's very humbling  and exciting to play a part in such a wonderful story that literally goes back to prehistory when Coober Pedy was a wilderness to opals becoming Australia's national gemstone.

"It's a great opportunity for everyone to learn this compelling story.

"As a state museum it is our job to bring new knowledge to people and to give people the chance to enjoy a truly unique show about one of the most precious gemstone in the world.

"I would encourage anyone who has the chance to see the exhibition.

"They won't be disappointed."

The exhibition will open on 25 September and closes 14 February 2016.

MORE INFORMATION

Adult $17
Concession $12
Child (under 16) $5
Family $35

See SA Museum 

The article brought to you in association with the South Australia Tourism Commission.