Knowledge article Australia's significant rock features

How old are Australia's rocks?

Australia has some of the oldest geological features in the world. The oldest known rocks date from more than 3,000 million years ago, while rare zircon crystals dating back 4,400 million years provide evidence of Australia's very ancient geological history.

These ancient features compare with some of the oldest known rocks on Earth, including rocks in north-western Canada that formed about 4,031 million years ago.

Australia also has much younger geological features. Some areas of Victoria and Queensland have been affected by volcanic activity that continued until a few thousand years ago. Australia's youngest mainland volcano is Mount Gambier in South Australia, which last erupted about 6,000 years ago.

Uluru, Northern Territory

Uluru is a massive sandstone rock formation in central Australia. Formerly known as ‘Ayers Rock’, it covers an area of 3.3 square kilometres, measures 9.4 kilometres around its base and rises 345 metres above the surrounding plain.

Uluru is the surface expression of a much larger volume of rock. It is an eroded remnant that was laid down in an inland sea during the Cambrian Period about 500 million years ago.

Earth uplift and folding about 300–400 million years ago tilted the rock to create its present vertical orientation from the original horizontal sedimentary strata.

Erosion of the surrounding area has left Uluru and nearby Kata Tjuta exposed. Both are within Uluru-Kata Tjuta National Park.

Kata Tjuta, Northern Territory

Kata Tjuta is a group of 28 rounded rock domes in the Northern Territory. Formerly known as ‘the Olgas’, the group includes Mount Olga, which rises 545.4 metres above the surrounding plain and is almost 200 metres higher than nearby Uluru.

The domes are made of sedimentary rock conglomerate with iron oxide impurities. The conglomerate resulted from the erosion of mountains pushed up during Earth movements and consists of sandstone, granite and ironstone bound together by muddy and sandy sediments.

Both features are within the Uluru-Kata Tjuta National Park.

Karlwe Karlwe, Northern Territory

Karlwe Karlwe, also known as the Devil's Marbles, is a collection of large, rounded granite boulders near Wauchope in the Northern Territory.

The granite formed from molten rock that solidified beneath a layer of sandstone and developed vertical and horizontal cracks. Over time, the sandstone eroded, exposing the granite, which then weathered into soft sand and clay surrounding hard blocks of granite called corestones.

Gradual removal of the soft sand and clay exposed the rounded boulders, allowing them to appear balanced on top of one another.

Mount Augustus, Western Australia

Mount Augustus is a large sandstone and conglomerate geological structure in Western Australia. The visible portion is twice the size of Uluru. It sits on a bedrock granite base, is about 8 kilometres long and stands 858 metres above the surrounding plain and 1,105 metres above sea level.

The rock of Mount Augustus is estimated to be about 1,000 million years old. The rock was formed from an uplifted remnant of ancient seabed of sedimentary Proterozoic sandstone and conglomerate.

The granite rock beneath Mount Augustus is said to be 1,650 million years old. The Indigenous name for Mount Augustus is Burringurrah.

Wave Rock, Western Australia

Wave Rock is a granite cliff in Western Australia that resembles a breaking ocean wave. Formed more than 2,700 million years ago, the rock is 14 metres high and 110 metres long.

The cliff forms the northern face of a large erosional remnant called Hyden Rock. The curved cliff face has been rounded by weathering and water erosion, which undercut its base, leaving a rounded overhang.

Wave Rock was formed by water dissolving and redepositing chemicals in the granite as it runs down the cliff face.

Gulaga (Mount Dromedary), New South Wales

Gulaga, also known as Mount Dromedary, is an isolated volcanic mountain on the New South Wales coast. It rises 797 metres above sea level near the historical villages of Tilba and Central Tilba.

The shape of the mountain resembles a dromedary camel. Gulaga was formed during volcanic activity about 100 million years ago.

Bald Rock, New South Wales–Queensland border

Bald Rock is an inselberg, or isolated rock hill, on the New South Wales–Queensland border. It is said to be Australia's largest exposed granite surface.

The granite dome is about 200 metres above the surrounding bushland, 750 metres long, 500 metres wide and rises to 1 277 metres above sea level.

The granite that forms Bald Rock was emplaced into the surrounding older metamorphic and sedimentary rock about 247 million years ago. Subsequent uplift and erosion removed most of the surrounding sediments and metamorphic rocks, leaving Bald Rock exposed because of its resistance to weathering.

Oldest known rocks in each state and territory

The oldest known rocks identified in each Australian state and territory vary considerably in age, rock type and geological setting.