A one tonne rock was taken from the Federation Rocks display at the National Rock Garden sometime between Thursday and Friday morning last week.
The rock, which would have required a truck or a ute-mounted crane to lift and remove, contained gold flecks and it is believed this is what attracted it to the thieves.
The Federation Rocks display was opened by ACT Chief Minister Katie Gallagher in October last year as part of Centenary of Canberra celebrations. The display consists of large rocks, the largest of which is 15 tonnes, from each state and territory.
"The missing rock was one of three rocks from the Bendigo goldfields in Victoria, chosen in recognition of the great historical significance of gold mining in Victoria," says Professor Brad Pillans, from the Research School of Earth Sciences, who is also Chair of the National Rock Garden.
"The rock probably contained less than half an ounce of gold, maybe a few hundred dollars' worth, distributed as fine particles through the rock. The thieves would have to crush the rock to extract the gold.
"Fortunately the display consisted of three separate pieces of rock, so we still have something to show people, but the stolen piece was the star exhibit because of the gold specks.
"This act has caused thousands of dollars of damage to a national monument, all for the sake of a few hundred dollars' worth of gold. I hope that the perpetrators are caught, and if it's not too late, that our missing rock can be recovered intact."
If you have any information about the missing rock, please contact Crime Stoppers on 1800 333 000 or via www.act.crimestoppers.com.au. Information can be provided anonymously.