Alex Tully discovers prehistoric reptiles and rocks in a scene reminiscent of Snow White.

The sight of a ferocious giant orange pterosaur spreading her wings protectively over a nest of thundereggs might have worried most people.

But for my younger son, who has had a deep fascination with dinosaurs, volcanoes and rocks since he was only 2, it was a welcome sign that we were on the right track.

We were already on holiday on Australia's Gold Coast when we discovered we weren't far from Thunderbird Mine, the world's largest source of the so-called thundereggs sometimes formed during volcanic eruptions, and there was no choice but to make like a Thunderbird and 3, 2, 1, GO.

This meant driving to the ancient volcano of Mt Tamborin where the pterosaur provided its fascinating welcome.


Normally we would have spent some time checking out this 200 million-year-old flying reptile, but we were eager to find some thundereggs of our own, so we said a quick hello to the pterosaur then hurried on to the rusting corrugated-iron shed signposted as the Rock Shop.

Here we were issued with mining permits, excavating picks, buckets, a safety talk and an explanation on what thundereggs look like from the outside.

As we marched off up the track to the mine in the required fully enclosed shoes, I had the strange feeling that we were re-enacting a scene from Snow White and the Seven Dwarfs and had the urge to sing "Hi ho hi ho. It's off to work we go".

When we arrived at the mine Grumpy dwarf didn't initially want to climb to the top, so the two of us began digging on the lower slopes of what looked more like a large pile of rubble than my idea of a mine. Doc and Happy dwarf followed the track higher up, where they methodically examined every rock in sight to see if it fit the criteria of a thunderegg.

Uncut thundereggs apparently look like a roundish rock with bumps on the outside, but I could not for the life of me find any. I guess that made me Dopey dwarf.

The rubble pile where we toiled away is the crumbling remains of a prehistoric volcanic lava flow and the thundereggs are the bubbles of gas (or "volcano farts", as my elder son christened them) caught in the solidifying lava.

According to the pamphlet, over the next 200 million years, as water seeped down through the lava, silica-rich minerals such as chalcedony, jasper, quartz and agate leaked into the empty pockets of space that the bubbles had left and solidified.

The resulting thundereggs, or spherulites as geologists call them, are unique and wonderful natural works of art.

After half an hour of digging, Happy became Hungry dwarf and I had developed a handful of blisters, so we marched back down to the corrugated-iron shed to empty our buckets on the dusty bench where many other treasure-seekers had dumped before us.

After casting a critical eye over our collection of rubble, resident thunderegg specialist Marty announced all of our findings were indeed thundereggs but most were too broken or too small to make cutting them open worthwhile.

Happy, who was now fed, asked for the tennis ball-sized only round rock in our collection to be cut open, while Grumpy, who was becoming Sleepy, was adamant that he wanted the much larger but partially broken thunderegg.

Our choices made, we peered through the glass window and watched the cutting process with anticipation while the buzzing of the diamond saws reverberated off the old iron walls.

A few minutes later, our 200 million-year-old mysteries were revealed. And we were not disappointed. Spirals and splotches in a range of shades and hues adorned our thundereggs with their own unique style.

So with prehistoric treasures in hand, we left Thunderbird Park and descended the mountain as happy little miners.

We even gave the orange pterosaur a wave goodbye.

Further information: Thunderbird Mine is at Cedar Creek, Mount Tamborine, on the Gold Coast. It is open daily from 9am-2.30pm and costs adults A$24 ($31) and children A$15.

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