Pumice is the only rock capable of floating on water.

Pumice is an extrusive volcanic rock that originates from explosive eruptions involving high-silica magma. When viscous lava is ejected, the sudden drop in pressure causes dissolved gases to expand rapidly, much like carbonation in a soda bottle. If the lava cools fast enough to solidify before the gas escapes, it creates a glass-like foam filled with tiny vesicles.The volume of these air-filled pores can account for up to 90 percent of the rock's total volume. Because the bulk density of pumice is lower than the density of seawater, which is approximately 1,025 kilograms per cubic meter, the rock remains buoyant. This unique property allows pumice to stay afloat for years as it drifts across the globe.A notable event occurred in 2012 when a massive pumice raft, roughly the size of Israel, was spotted near New Zealand after the Havre Seamount eruption. Researchers from the University of Tasmania and other institutions have studied these rafts to understand how they facilitate the migration of species like barnacles, mollusks, and crabs. Over time, water gradually infiltrates the pores through capillary action, eventually causing the rock to lose buoyancy and sink to the ocean floor.