Pumice

Physical Properties

Hardness: 5-6 (but very brittle), Color: white to light gray, Luster: dull to silky, Crystal Structure: amorphous (glassy), Specific Gravity: <1.0 (floats on water), vesicular texture.

Formation & Geological History

Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected and cools rapidly, trapping gas bubbles (vesicles) in a glassy matrix. Most deposits are Cenozoic to recent.

Uses & Applications

Abrasives (pumice stones), lightweight concrete aggregate, horticulture (soil aeration), beauty products (exfoliation), and stonewashing denim jeans.

Geological Facts

Pumice is the only rock that can float on water due to its low density and air-filled pores. Large eruptions can create 'pumice rafts' that travel across oceans for years.

Field Identification & Locations

Identify in the field by its sponge-like appearance, extreme light weight, and light color. Often found near cinder cones and volcanic ash deposits in regions like Italy, the USA, and New Zealand.

Identified on: 5/3/2026

Mode: Standard