Intrigued, they took a closer look and Leon Wright, thinking it could have been some kind of cyst from a large marine animal, suggested they take the 14.75 kg (32 lb) lump home.

"She said 'You're not putting that thing in my car'," the Australian Broadcasting Corp. quoted marine ecologist Ken Jury as saying on its Web site (www.abc.net.au) on Wednesday.

Curiosity eventually got the better of the Wrights. Unable to find an answer on the Internet, they went back and got it two weeks later and described it to Jury.

"It immediately struck me as being ambergris -- it couldn't be anything else," Jury said.

"It's actually belched out by the animal, would you believe, and those few across the world that have witnessed that or heard it say it's quite remarkable ... apparently the sound of it travels for miles across the water," he said.

Jury, who is acting for the family, said ambergris can fetch between $20-$65 a gram, The Age newspaper reported on Wednesday. That would make the Wrights' find worth at least $295,000.

Used in perfumes by ancient Egyptians and mythologised in literary classics like Herman Melville's "Moby Dick", ambergris is spewed out of the intestines of sperm whales.

Scientists theorise it is produced to aid in the removal of hard, sharp objects like squid beaks that whales may eat.

The waxy, foul-smelling substance is lighter than water and can float for years, during which time it is cleansed by the sun and salt water and becomes hard, dark and waxy and develops a rich musky smell prized by perfumers around the world.