Pumice

Hardness: 5-6 Mohs (though brittle), Color: Light gray/white/cream, Luster: Vitreous to dull, Crystal Structure: Amorphous/Vesicular, Specific Gravity: 0.25-0.9 (floats in water)

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, creating a frothy glass structure with trapped gas bubbles (vesicles). Found in volcanic regions worldwide across various geological eras.

Used as a mild abrasive in personal care (pumice stones for skin), as a lightweight aggregate in concrete, in laundry for stone-washing denim, and in horticulture for soil aeration.

Pumice is the only rock that can float on water due to its incredible porosity. Massive 'pumice rafts' can form after submarine eruptions, traveling thousands of miles across oceans.

Identify in the field by its extreme lightness (low density), vesiculated (bubbly) texture, and light color. It is common on beaches near volcanic islands and in ash-fall deposits.