A US woman bit down on a rare pearl while eating a meal of clams at an Italian restaurant.

KOMO-TV reports Lindsay Hasz and her husband Chris were eating at Montalcino Ristorante Italiano in Issaquah, Washington state, recently when she bit into something hard in her entree.

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Hasz says she wasn’t sure what it was but put it in her pocket and went home to do research.

She took it to a gemologist, who determined it was a Quahog purple pearl worth about $US600 ($A832).

Ted Irwin of Northwest Geological Laboratory says the find is rare, with only one in two million being of gem quality.

Montalcino owner Cindy Nardone says she’s happy for Hasz.

Hasz says she may have the pearl made into a necklace.