PILES of grey, porous stones have washed up on Kingscliff Beach over the past few days.
Despite speculation across social media that it may have been dead coral washed in by heavy swells, Southern Cross University geologist Dr Malcolm Clark said the stones were probably volcanic pumice.
"If it's pumice it is a vesiculated igneous rock," he said.
"On the east coast if you see it, it likely comes from Vanuatu and Fiji.
"Their volcanos, especially in Fiji...produce a lot of pumice."
Alternatively, Dr Clark said the pumice could have been sitting on our beaches for a long period of time, and due to excess sand being washed away, ended up surfacing.
"It may be that the heavy erosion uncovered pumice that was already there," he said.
"The ones that were under the sand may have been recycled because it's so light that it just comes up and floats up onto the beach."
"I highly doubt that it is coral reef."
Dr Clark said as large swells continued up the coast more pumice could end up washed onto Tweed beaches.