I found the rock on the beach. It has a redish hue and floats on water. It feels as though it is hollow because it is light for its size. Does anyone have an idea what this is?enter image description here

  • $\begingroup$ you sure its not plastic? $\endgroup$
    – John
    Commented Aug 5, 2018 at 14:47
  • 1
    $\begingroup$ Rocks usually do not float on water. The only rocks that float on water are very porous rocks like pumice. $\endgroup$
    – Gimelist
    Commented Aug 6, 2018 at 10:30

1 Answer 1


This isn't a rock at all, but a seed of Entada Gigas, sometimes called the sea heart or sea bean.

Entada Gigas seeds (CC-BY-SA-3.0)

Entada Gigas is called the "sea bean" for good reason: it's a member of the bean family Fabaceae. In fact, this species has the family's largest seed, a flattened heart shape 6 cm in diameter and 2 cm thick. These hollow seeds are washed into the ocean and drift on currents for up to 2 years, on the chance that one will wash up somewhere to germinate. It seems that sea beans have evolved to propagate in this way, similar to coconuts.


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