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Australia’s five best rocks for budding geologists



A Monash University affiliate and scientist at the Australian Nuclear Science and Technology Organisation (ANSTO) has described the five most interesting rocks to be found on Australian soil.

Emily Finch penned the article for The Conversation, stating that each rock represents not just a period in the Earth’s history, but a significant time in our own.

The first of the “five rocks any great Australian rock collection should have” was a Mantle xenolith.

“The youngest rocks in Australia are those that erupted out of Australia’s youngest volcano in Mount Gambier, South Australia, 4000 to 8000 years ago,” Finch writes.

“That volcano is the culmination of an enormous field of volcanoes that span central and western Victoria.”

Victoria has been scarcely known for its volcanic activity but a ring of the geological formations was the cause of mantle xenoliths.

While magma rose from between the Earth’s core and crust – the mantle – it brought pieces of the mantle with it from almost 3km deep.

These black or brown rocks were consequently named mantle xenoliths and hold inside them a surprising piece of green mineral, like a big geological seed.

Finch awarded second place to meteorites – often found in the Nullabor, South Australia and Western Australia.

“The dry environment is ideal for preserving meteorites that fall to Earth, and the light colour of the limestone country rock and lack of vegetation means the black and brown meteorites are easier to see,” Finch writes.

These space-spawned rocks can be found using magnets and have been known to hold up to 40,000-year-old secrets.

Broken Hill is home to Finch’s third favourite Australian rock – the metamorphic kind.

Metamorphic rocks begin as sand and mud and are slowly compressed by years of extreme heat and compression underground – reaching more than 700℃ below the surface.

This process brings a stripey, “garnet-rich” sample to the rock for geologists to marvel at.

The fourth edition to this list comes as a rock formation – namely, a banded iron formation.

These are commonly found in Western Australia and may be harder to take home.

They will display alternating layers of chert which is made of quartz and as is the norm in WA will show-off deep reds, silvers and blacks.

“The Hamersley Province in the northwestern part of Western Australia has the thickest and most extensive banded iron formations in the world. They are about 2.45 to 2.78 billion years old,” Finch writes.

“Banded iron formation is exciting because it no longer forms on Earth today, meaning it records an ancient process that we no longer see happening.”

The bands are thought to have formed in the oceans where continental shelfs expanded out from the land and fell away to the ocean floor.

Finally, on Finch’s list of Australia’s best rocks, are dinosaur fossils.

Central and western Queensland are good for these discoveries, according to Finch, if you want to get a glimpse into life up to 250 million years ago.

“If you’re really lucky, you might even have dinosaur bones on your property, like the huge, long-necked sauropod discovered just this year on a Queensland cattle farm,” Finch concluded.

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