Pumice

Physical Properties

Hardness: 5-6 (but brittle), Color: grayish to dark gray/black (scoriaceous), Luster: dull to vitreous, Structure: vesicular (pitted with gas bubbles), Specific Gravity: 0.25 to 0.7 (often floats on water).

Formation & Geological History

Formed during explosive volcanic eruptions when pressurized lava is violently ejected. The rapid cooling and depressurization cause gas bubbles to be trapped in the solidifying rock, creating a frothy texture.

Uses & Applications

Used as an abrasive in cleaning and personal care (pumice stones), in lightweight concrete production, as a landscaping material, and in stone-washing textiles like denim.

Geological Facts

Pumice is the only rock that can float on water due to its low density and high porosity. Large 'pumice rafts' can form on the ocean after underwater volcanic eruptions and drift for thousands of miles.

Field Identification & Locations

Identify in the field by its extreme lightness, coarse vesicular texture, and ability to float. Commonly found in volcanic regions such as the Cascade Range (USA), Italy, and Iceland.

Identified on: 4/22/2026

Mode: Standard