Mount Hay

via Rockhampton
S 23’26.628, E 150’26.315

Nestled at the base of Mt Hay, on what was once a rumbling volcano and the thudereggs you admire today are the fruits of its violent eruptions – “Volcanic Birthstones”. Ordinary on the outside, these geo treasures are stunning underneath and their layers tell the story of an incredible geo journey.

What are Thundereggs?

Hot Beginnings… Mt Hay’s thundereggs formed in silica-rich volcanic rocks resulting from ancient lava flow called Rhyolite 120 million years ago.

Trapped in Time… The flowing Rhyolite trapped small particles and tiny gas bubbles, leading to the development of ‘volcanic birthstones’.

Formation… Thundereggs occurred when two forms of crystallization took place creating spherulites and spheruloids. Spherulites are a radical growth created when minerals crystallize around a nucleus. Spheruloids are a hollow form created when minerals crystallize around a steam bubble.

Stars in the Stone… As the lava cooled the star shaped cavity often seen in thundereggs (spheruloids) developed.

Lasting Layers… The cooling caused minute cracks to occur, allowing silica-rich solutions to seep into the cavities. This filled them with minerals such as quartz, agate, chalcedony, quartz crystals, amethyst, jasper and opalite.

Due to weathering over the past 120 million years has exposed these volcanic wonders.

How Can I Experience Mt Hay?

Fossick for ‘Volcanic Birthstones’
Try your luck and take home your geo treasure! Tools and assistance provided. A truly fascinating experience.

Take a Guided Tour
Explore the thunder egg site and check out the gemstone cutting and pewter casting factories.

Camp with Thundereggs 
Camp amidst this intriguing landscape, surrounded by the secrets of the ages.

For more information
Contact Mt Hay Gem Tourist Park for more information about tours and fossicking (Phone: 07 4934 7183).


Heading West
See the breathtaking sandstone plateau rising above Central Queensland’s plains at Blackdown Tableland National Park. Stop at Blackwater, the Coal Capital of Queensland and home to the International Coal Centre. Enter the Central Highlands and see Emerald’s fossilised tree trunk estimated to be 250 million years old, and then carry on to the Sapphire Gemfields.Your next geo-stop, heading west:
Blackdown Tableland National Park
Heading East
Rockhampton is the gateway to the Capricorn Coast. Admire the picturesque headlands at Yeppoon and the twin peaks of Double Head, dramatic examples of ancient volcanic plugs. Take a walk to Fan Rock, an unforgettable site showing the effects of cooling on a plug; and explore the Great Barrier Reef, one of the world’s seven wonders.Your next geo-stop, heading east:
Capricorn Caves, The Caves