Key points
- Fossicking reveals the layered history beneath our feet through gem and mineral discovery.
- Sapphires are prized finds. Trace elements in the gems paint them in hues that range from deep blues to vibrant pinks.
- Fossicking fields can be found along the eastern states of Australia but research local state rules before you go.
A winter fossicking holiday in the cold Central Tablelands in New South Wales? The idea didn’t immediately spark joy in Dr David Miljak’s family. However, thanks to some beginners’ luck, they unearthed a load of gem-quality sapphires on their first dig.
“That was 10 years ago. Since then, we’ve found numerous gem-quality sapphires, and other beautiful minerals like coloured zircons,” David says.
A popular hobby, fossicking involves looking for valuable stones and minerals. Often, a good place to start looking is where these gemstones were once dug from the ground.
David admits there is no guarantee of striking it lucky.
“Sometimes it’s a case of throwing a rock over your shoulder and digging where it lands,” David says.
David does concede that there are specific areas that are more likely to yield mineral treasures.
“Understanding how the minerals are formed and transported helps narrow the search area.”
He concentrates on the shallow alluvial layers beneath the topsoil. These layers were deposited by ancient streams and rivers. They contain a rich mixture of rocks and minerals...including the odd sapphire.
Volcanic origins of sapphires
The word sapphire comes from a Greek word Sapheiros, and the Latin word Saphirus, meaning blue.
Sapphires are formed out of a mineral called corundum. Corundum is composed of aluminium oxide (Al2O3). It is one of the hardest natural substances, second only to diamond.
During volcanic processes, igneous or metamorphic rocks endure tremendous heat and pressure. This melts the corundum in their structures. These rocks are rich in aluminium but low in silicon. As they slowly cool, the molten corundum seeps into cracks and solidifies into colourless crystals.
So, where do sapphires get their colour?
Coloured by trace elements
The colour of corundum depends on the presence of trace elements or impurities.
We know sapphires are blue. But they can also be green, yellow, orange, pink, purple or black.
The colour depends on the amount and type of other elements in the crystal. Blue sapphires contain titanium and iron. Chromium gives a pink colour. More chromium creates a ruby.
“The Australia Museum in Sydney has an amazing collection of gems and minerals which I highly recommend,” David says.
Fossicking for fun
It’s a simple hobby to begin.
“All you need are very simple hand-tools, like a shovel, pick and sieve, and perhaps a ‘mud map’ of the fossicking area to get started,” David says.
There are gem fossicking fields at specific sites along the Great Dividing Range in the eastern states of Australia and in Tasmania. Some of these are designated public fossicking areas.
But it is important to know the local state rules. Fossicking is not permitted or is restricted in many areas so make sure you do your research. Some areas may require a state licence. A quick search of state government websites will provide the information you seek.
“It’s important to abide by the fossicking rules, so everyone can continue to enjoy the pastime,” David says.
Another tip David offers for beginners is to start where previous fossickers have been.
“Knowing other people have found something in the location is a good sign. Also, a dose of luck, patience and good humour helps,” David says.
Detecting mineral signatures
David leads our research developing advanced sensor technologies, used to enable bulk sorting of mineral ores and process control.
His own work involves detecting ‘mineral signatures’. These are unique radio signals that relate to the presence of certain minerals in rocks.
He even uses some of his fossicking finds to assist his research.
“The team scanned some gem-grade zircon specimens found in the NSW Central Tablelands. We were able to capture the unique zircon mineral signature,” David says.
But that is not the hook for the hobby. David has developed a deep fascination with the beauty of these gemstones and other minerals.
“It becomes addictive, immersing yourself in nature and uncovering the beauty of natural sapphires.”