Pumice

Hardness: 5-6 (Mohs scale), Color: light gray to cream, Luster: dull to vitreous, Texture: vesicular (highly porous), Specific Gravity: low (often floats on water)

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles (vesicles), creating a frothy, glass-like texture.

Used as an abrasive in polishing, skin exfoliation (pumice stones), heavyweight concrete additive, and in denim stone-washing.

Pumice is the only rock that can float on water until it eventually becomes waterlogged. Massive 'pumice rafts' can travel across oceans for years after an eruption.

Identified by its extremely lightweight feel and presence of thousands of tiny holes (vesicles). It is commonly found in areas of recent volcanic activity such as Iceland, Italy, or the Pacific Northwest.