igneous

Pumice

Vesicular volcanic glass

Hardness: 5-6 (Mohs scale), Color: light gray to cream, Luster: dull to silky, Crystal Structure: amorphous (glassy), highly vesicular (filled with air bubbles), very low specific gravity (often floats on water).

Identified April 13, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected into the air, cooling rapidly and trapping gas bubbles as it solidifies. Primarily found in volcanic regions of various ages.

Uses & applications

Used as an abrasive in cleaning products, skin exfoliants (pumice stones), lightweight aggregate in concrete/cinder blocks, and in stonewashed denim production.

Geological facts

Pumice is the only rock that can reliably float on water for long periods. Large eruptions can create 'pumice rafts' that drift across oceans for thousands of miles.

Field identification & locations

Identify by its extremely lightweight feel and sponge-like texture with visible holes (vesicles). Found in volcanic fields, beaches near volcanic islands, or as decorative landscaping stones.

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