Pumice

Physical Properties

Hardness: 5-6 (but brittle and easily crushed); Color: White, cream, or light gray; Luster: Dull or pearly; Structure: Vesicular (bubbles) and glassy; Specific Gravity: Very low (floats on water)

Formation & Geological History

Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected into the air. The rapid cooling and depressurization trap gas bubbles, creating a sponge-like texture.

Uses & Applications

Used as an abrasive in skincare (pumice stones), in industrial polishes, as a lightweight aggregate in concrete, and for horticultural soil amendments.

Geological Facts

Pumice is the only rock that floats on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that travel thousands of miles across oceans.

Field Identification & Locations

Identify in the field by its perforated, sponge-like surface and its extreme lightness. It will feel much lighter than any other rock of equivalent size. Commonly found near explosive volcanoes.

Identified on: 4/17/2026

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