igneous

Pumice

Pumice (Vesicular Volcanic Glass)

Hardness: 5-6 (Mohs scale); Color: Light gray, tan, or white; Luster: Pearly to Vitreous; Crystal structure: Amorphous (non-crystalline glass); Cleavage: None; Specific gravity: 0.25 to 0.7 (floats on water); Texture: Highly vesicular (pitted with tiny holes).

Hardness: 5-6 (Mohs scale)
Color: Light gray, tan, or white
Luster: Pearly to Vitreous

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when gas-rich, frothy magma cools very rapidly, trapping gas bubbles (vesicles) as the rock solidifies. It is primarily associated with felsic magmas rich in silica.

Uses & applications

Used as an abrasive in polishing and personal care (pumice stones), lightweight aggregate in concrete/cinder blocks, a soil amendment in horticulture, and in stone-washing processes for denim.

Geological facts

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

Field identification & locations

Identify in the field by its extreme lightness, porous texture, and ability to float. Commonly found in regions with explosive volcanic history such as Italy, Greece, the Pacific Northwest (USA), and Iceland.

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mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous