Pumice

Hardness: 5-6 (but brittle), Color: Light gray to white/cream, Luster: Dull or pearly, Structure: Highly vesicular/porous, Density: Very low (often floats in water).

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles, creating a frothy texture. Found in areas of active or recent rhyolitic volcanism.

Used as an abrasive in soaps (pumice stones), cosmetic exfoliants, dental polishing, and stone-washing textiles like denim. Also used as a lightweight aggregate in concrete and as a soil conditioner.

Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. During massive eruptions, floating pumice rafts can stretch for miles across the ocean.

Identify in the field by its extreme lightness (low specific gravity) and visible pores. Commonly found near volcanoes or on beaches where it has washed ashore. Collectors value unique shapes or pure colors.