Mystery Stones That Float Wash Up On Jersey Shore

LONG BRANCH, NJ — Clean Ocean Action, a volunteer group that leads the clean-ups of Jersey Shore beaches every spring, said thousands — "possibly hundreds of thousands" — of these small, gray stones washed up on NJ beaches from Pier Village to Sandy Hook last week.

The group described the stones as "pumice-like, lightweight ... a few pieces can easily fit in the palm of a hand, and they float! Some pieces appear smoothed or shaped, with faint grid-like marks, suggesting they may be man-made."

Clean Ocean Action said their theory is the stones were used in industrial, water or wastewater filtration systems, and made their way into the ocean during recent heavy rains.

The NJ Department of Environmental Protection has been notified, but as of Tuesday the agency has not said what the rocks may be.

"A concerned citizen helped identify what it could be: foamed glass aggregate," Clean Ocean Action said Tuesday.

Clean Ocean Action will hold their Spring 2025 Beach Sweeps this Saturday, April 12. The clean-ups will be held at more than 80 beaches, lakes, parks and streams across New Jersey, all from 9 a.m. - 12:30 p.m. this Saturday. You or your group can sign up here to participate.