Cape Hillsborough geology

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.