Portia Himsel thought she had found a marble in a shell while playing at a Banks Peninsula beach on Boxing Day, but she may have stumbled on one of New Zealand's most valuable pearls.
The Halswell 6-year-old was at the water's edge at a bay near Birdlings Flat when a partly opened grey shell caught her eye.
"I threw a rock at it and it didn't move," she said.
"That's why I opened it up and I saw the pearl. I didn't really think much when I saw it.
"I thought it was a marble. I pulled it out and showed Mum and Dad."
Her father, Daniel Himsel, said they initially had trouble believing it was the real thing.
"It seems perfectly round. That's why we didn't think it was real, but she said she found it in a shell," he said.
"I don't know anyone who's ever found a pearl before."
Portia waited some time before showing her father, mother Megan and sister Claudia, 9, her find.
Daniel Himsel said Portia first held the pearl in her hand for safekeeping and then left it in the pocket of a tent.
"We've taken better care of it since," he said.
Roger Beattie, of Eyris Blue Pearls in Christchurch, said Portia's pearl "could be the find of the year".
"I've never seen a good-quality large oyster pearl in New Zealand," he said.
"It's got good lustre, it's a white pearl. It's smooth and it's large and it looks pretty round."
The pearl, 12 millimetres in diameter, would be worth thousands of dollars to the right collector, he said.
"This is what they call a free pearl.
"Free pearls are worth more than one that's attached to the shell.
"And it's a natural pearl, which is worth more than cultured pearls," he said.
"My guess is it's from a New Zealand oyster shell. I would call it double-A probably. It's good quality."
AAA is the highest grade of pearl.
The Himsels have not decided what they will do with the pearl but will consider getting it valued.