Mid to late 1970s necklace made of small round white shells.
Worn by surfers, it caught on and was a big fad. Worn usually snug around the neck; they were a status symbol until about 1980; they came back in style for a short time many years later.

A Puka Shell Necklace is the same thing as a "pearl necklace", only in an undisturbed and now dried state.