The sandstone and quartz rock from a gold mine in Bendigo was stolen on Thursday night. It featured large veins of quartz running through it along with small flecks of gold.

It was stolen from the National Rock Garden, on Lady Denman Drive near the National Arboretum, sometime on Thursday night. The theft was noticed 10am Friday.

Police said the rock was one metre long, 75cm high and a triangular shape. It is grey and brown in colour, with prominent bands of white quartz.

National Rock Garden chairman Brad Pillans believed the rock had been stolen to extract the gold and described the act as "sickening".

"It's just foolishness," he said. "It's stupidity on the part of the people who have perpetrated the act for thousands of dollars of damage to a display for the yield of a few hundred dollars of gold."

Mr Pillans said the thieves would be able to get a half ounce of gold at most from the rock.

He said the rock weighed about a tonne and would have required a truck with a mounted crane to remove it from the display.

The rock was donated to the National Rock Garden by the Unity Mining company and the Victorian government, and was the only rock in the garden that contained gold.

He appealed to the public to help find the rock, saying the theft would have been very noticeable.

"If someone has stolen it to have it sitting in their garden, that’s pretty silly because it’s pretty recognisable," he said.

"It’d be lovely if someone looked over their fence and spotted it."

The stolen rock was part of the National Rock Garden's Federation Rocks display, which was opened by Chief Minister Katy Gallagher in October 2013 to celebrate the centenary of Canberra.

The display was designed to commemorate Australia's federation. Each state donated a number of rocks that symbolised their history.

Police ask anyone with more information about the theft to contact Crime Stoppers on 1800 333 000 or via www.act.crimestoppers.com.au.