Pumice

Physical Properties

Hardness: 5-6 Mohs (though fragile), Color: White to light grey, Luster: Dull to pearly, Structure: Highly vesicular (honeycombed with bubbles), Specific Gravity: 0.25 to 0.9 (floats in water).

Formation & Geological History

Formed during explosive volcanic eruptions where highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization create a foamy glass structure. It is found in volcanic regions globally.

Uses & Applications

Used as a lightweight aggregate in concrete/cinder blocks, as an abrasive in polishing, in skincare for exfoliating (pumice stones), and in stone-washed denim production.

Geological Facts

Pumice is the only rock that can float on water due to its air-filled pores. After large volcanic eruptions, massive 'pumice rafts' can form on the ocean and float for years.

Field Identification & Locations

Identify by its incredibly light weight, abrasive texture, and high porosity. It will easily scratch softer materials but crumble if struck hard. Found in areas with history of rhyolitic or dacitic volcanism.

Identified on: 5/1/2026

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