igneous

Pumice

Pumice (Vitreous volcanic rock)

Hardness: 5-6 Mohs (though fragile due to porosity); Color: White, cream, tan, or grey; Luster: Dull to pearly; Structure: Vesicular (highly porous/bubbly); Specific Gravity: 0.25-0.9 (floats in water).

Hardness: 5-6 Mohs (though fragile due to porosity)
Color: White, cream, tan, or grey
Luster: Dull to pearly

Identified March 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles, creating a solidified froth of volcanic glass.

Uses & applications

Used as an abrasive in soaps (pumice stones) and polishes, in lightweight concrete production, as a horticultural soil amendment, and in the 'stone-washing' of blue jeans.

Geological facts

Pumice is the only rock known to man that can float on water indefinitely until it becomes waterlogged. Large 'pumice rafts' from underwater volcanoes can drift across oceans for years.

Field identification & locations

Identify in the field by its extremely light weight and 'frothy' appearance filled with tiny holes (vesicles). It is commonly found in areas of recent or historic explosive volcanism such as the Andes, Italy, or the American Northwest.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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