How volcanic foam becomes a foot scrubber
Pumice begins in magma—molten rock beneath Earth’s surface—that contains dissolved gases. As the magma rises and pressure drops, those gases expand into bubbles, much as carbon dioxide fizzes out of a newly opened drink. In a gas-rich eruption, the melt can become a frothy mass rather than a dense stream of lava.
The bubbles become pores
If that froth cools and hardens before its bubbles can escape or collapse, the rock preserves them as a network of holes. These spaces, called pores, make pumice unusually light for a solid rock; some pieces can float until water gradually fills the pores.
The same structure gives pumice its scrubbing texture. Its rough surface and exposed pore edges can wear away thick, dead skin when rubbed gently over a callus. It is not a chemical treatment: the stone works by abrasion, so pressing hard or scrubbing cracked or irritated skin can cause injury.
A useful tradeoff in the rock
Pumice’s usefulness comes from a volcanic process that leaves the material full of empty space. The trapped bubbles weaken the rock compared with solid lava, but they also make it light and naturally abrasive. A chunk formed in a rapidly cooling eruption can therefore serve as a simple tool for smoothing skin—provided the roughness is used with care.
