In 2015, David Hole was prospecting in Maryborough Regional Park near Melbourne, Australia.

Armed with a metal detector, he discovered something out of the ordinary – a very heavy, reddish rock resting in some yellow clay.

He took it home and tried everything to open it, sure that there was a gold nugget inside the rock - after all, Maryborough is in the Goldfields region, where the Australian gold rush peaked in the 19th century.

To crack open his find, Hole tried a rock saw, an angle grinder, a drill, even putting the thing in acid, but not even a sledgehammer could make a crack. That's because what he was trying so hard to open was no gold nugget. As he found out years later, it was a rare meteorite.

Unable to open the 'rock', but still intrigued, Hole took the meteorite into the Melbourne Museum to be identified.

"I've looked at a lot of rocks that people think are meteorites," Melbourne museum geologist Dermot Henry told 10 daily.

In fact, after 37 years of working at the museum and examining thousands of rocks, Henry explains only two of the offerings have ever turned out to be real meteorites.

This was one of the two.

It's a huge 17 kilograms (37.5 pounds), and after using a diamond saw to cut off a small slice, they discovered its composition has a high percentage of iron, making it a H5 ordinary chondrite.

Once open, you can also see the tiny crystallised droplets of metallic minerals throughout it, called chondrules.

The researchers argue that the Maryborough meteorite is much rarer than gold. It's one of only 17 meteorites ever recorded in the Australian state of Victoria, and it's the second largest chondritic mass, after a huge 55-kilogram specimen identified in 2003.

Now is probably as good a time as any to check your backyard for particularly heavy and hard-to-break rocks - you might be sitting on a metaphorical gold mine.