USGS demonstrates a floating rock
U.S. Geological Survey
A USGS demonstration shows pumice floating in water while other rocks of similar size sink, explaining the difference through density.
Based on: U.S. Geological Survey
Verdict
True
Verification confidenceHigh
Explanation
Yes. Some rocks can float on water. Pumice, a porous volcanic rock, provides an example: gas-filled spaces can make the rock as a whole less dense than water.
The USGS demonstrates pumice floating while other rocks sink. A 2025 experimental study of pumice from Sakurajima also documented floating samples and investigated how their pores admit water.
This does not mean every piece of pumice floats or remains afloat indefinitely. The study found substantial differences between samples, with some sinking almost immediately and others floating for more than ten days. Pore structure and water infiltration matter.
Key takeaway
Being a rock does not guarantee sinking. Pumice can float, but its buoyancy depends on its pores and how much water enters them.
Evidence
Supports the claim
Experiments document floating pumice
Riko Nagao, Tadashi Yokoyama and Shingo Takeuchi
The researchers immersed pumice samples in water and measured their flotation, directly documenting that some samples remained afloat.
Based on: Progress in Earth and Planetary Science
Flotation duration varies between samples
Riko Nagao, Tadashi Yokoyama and Shingo Takeuchi
The study linked differences in flotation duration to pore characteristics and water infiltration; it does not establish a universal duration for pumice.
Based on: Progress in Earth and Planetary Science
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