Pumice

Physical Properties

Hardness: 5-6 (but very brittle); Color: Cream, light gray, or tan; Luster: Dull to silky; Structure: Highly vesicular/cellular; Specific Gravity: Below 1.0 (it floats in water).

Formation & Geological History

Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected into the air, cooling rapidly and trapping gas bubbles.

Uses & Applications

Used as an abrasive in soaps, foot scrubs (pumice stones), and industrial polishing. Also used in lightweight concrete and horticultural soil mixes.

Geological Facts

Pumice is the only rock that can float on water due to its high porosity. Large eruptions can create 'pumice rafts' that drift across oceans for years.

Field Identification & Locations

Identify by its light weight and 'frothy' appearance. It is commonly found near volcanic arcs and subduction zones like the Cascades or the Mediterranean.

Identified on: 5/17/2026

Mode: Standard