Cape Hillsborough geology
GEOLOGY
Cape Hillsborough – the youngest volcanic area in Australia – was formed 30 million years ago. Volcanoes erupted along the coast from Proserpine to Mackay, creating the dramatic rock formations that frame Casuarina Bay.
Even if you don’t know much about geology or mineralogy, you’ll no doubt be amazed by the results of volcanic upheaval as you wander along our beautiful beaches. This upheaval led to the formation of geologically diverse landscapes, featuring distinct lava seams separated by layers of volcanic ash and pyroclastic materials.
The cape itself is a rugged headland of volcanic rock that towers dramatically 268 metres above sea level. Wander along the coast, and you’ll find many caves and overhangs also formed out of volcanic activity. Five kilometres west of the main visitor area is find Pinnacle Rock, the core of an extinct volcano (known as a trachyte plug) active around 32 million years ago.
At the bottom of our shallow freshwater lakes are limestone beds containing 33-million-year-old fossils of ancient turtles and crocodiles. To see a breathtaking example, visit the seaward side of the northern end of the causeway to Wedge Island at low tide. You might spot shells (ostracoda), molluscs (gastropoda), fish spines (teleostei), turtle and fish fragments (chelidae) and crocodile fragments (crocodylidae and coprolites).
Other rock formations to explore include coarse-grained granites at McBrides Point, and limestone and oil shales near Wedge Island.
MINERALS
Although Cape Hillsborough’s geology is diverse, it is dominated by rhyolite, an acidic volcanic rock that erodes into shallow, stony soils. It contains a lot of mica, a grey mineral with a shiny, golden surface. To spot it, look out for golden flecks that sparkle both in the fine, dark sands on our beaches and in the waves. Mica is used commercially in electronics, and, according to folklore, walking on mica in bare feet can help with arthritis, stiff joints and headaches.
Another two minerals found in abundance on our beaches are the gemstones chalcedony and agate, which are types of quartz. You can recognise them by their translucence, and will likely see them in pebbles along the beach and in rock seams. Agate has fine colourful bands, while chalcedony has no bands, but feels waxy when rubbed. Chalcedony and agate are used in jewellery, and, according to folklore, can purify the blood and have a calming effect when held.
Less often, you’ll find cornelian, a rarer type of quartz. It’s blood red in colour, which is the result of iron oxide, and you’ll find it on the Causeway and around Wedge Island. Cornelian is used for ornamental purposes.
You’ll also find plenty of pumice stone at Cape Hillsborough, especially along the high tide line in Beachcombers Bay. It’s grey, porous and lightweight, and you can use it to treat calluses and cracks on your feet and elbows. In the same spot, look out for leopard stone, a volcanic conglomerate marked with yellow spots.
An even more striking formation around the area is the thunder egg. This is an egg-shaped agate containing crystals. If you’re keen to see on, try searching the high tide line between Beachcombers Bay and Indian Head – but when the tide is low.
Finally, you might see topaz, as well as opal and shale oil, on the beach at the southern end of the causeway.
We hope you enjoy exploring the many diverse minerals in and around Cape Hillsborough, but please leave them where you see them. It is illegal to remove any materials from a national park.