Pumice

Physical Properties

Hardness: 5-6 Mohs (though very fragile); Color: light gray to cream; Luster: earthy or dull; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: less than 1.0 (floats in water).

Formation & Geological History

Formed during explosive volcanic eruptions when lava is ejected into the air. The rapid cooling and depressurization trap gas bubbles, creating a frothy, glassy texture. Found in areas of recent or past volcanic activity.

Uses & Applications

Used as an abrasive in cleaning products, exfoliating stones for skin care (pumice stones), lightweight concrete aggregate, and in stone-washing processes for denim jeans.

Geological Facts

Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice can drift for thousands of miles across oceans after major eruptions.

Field Identification & Locations

Identify in the field by its light weight (low density) and the presence of numerous tiny holes or vesicles. Found in subduction zones and volcanic arc environments. Collectors value it for educational purposes.

Identified on: 4/22/2026

Mode: Standard