A quartz rock weighing three-quarters of a tonne has been stolen from the National Rock Garden in Canberra.

The National Rock Garden is designed to showcase rocks from all over Australia.

The stolen rock from Bendigo was donated by a mining company to symbolise Victoria's gold rush history.

Rock Garden chairman Brad Pillans says flecks of gold in the rock may have attracted thieves.

"They've trucked the rock away. They may well try to crush it up and extract the gold," he said.

"The silly thing is they've caused thousands of dollars of damage to the exhibition and taken a rock which will be very difficult to replace, all for perhaps $200 worth of gold."

Professor Pillans says some of the rocks in the garden are up to 16 tonnes in weight.

"The display actually consisted of three rocks, one of which is six tonnes, so that wasn't touched," he said.

"But the most spectacular rock, which was actually mounted on top of the larger rock and secured with three metal pins, would have required a crane."

Professor Pillans is urging Canberrans to keep an eye out for the rock which is predominantly white in colour.

"It would be a bit unusual for your neighbour to turn up with a big white rock," he said.

"If someone's seen a big white rock unloaded in someone's front garden we'd like to hear about it."