igneous

Pumice

Pumice (a highly vesicular volcanic rock)

Hardness: 5-6 (but fragile); Color: light gray to cream; Luster: dull to silky; Crystal structure: amorphous/glassy; Cleavage: none; Specific gravity: 0.25 to 0.9 (floats on water).

Hardness: 5-6 (but fragile)
Color: light gray to cream
Luster: dull to silky

Identified May 7, 2026More igneous →

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Physical properties

Hardness: 5-6 (but fragile); Color: light gray to cream; Luster: dull to silky; Crystal structure: amorphous/glassy; Cleavage: none; Specific gravity: 0.25 to 0.9 (floats on water).

Formation & geological history

Formed through rapid cooling and depressurization of gas-rich silica-rich lava during explosive volcanic eruptions. Typical of Plinian eruption events.

Uses & applications

Used as an abrasive in cleaning products, cosmetic exfoliants, concrete additives (pozzolan), and in stone-washing textiles like jeans.

Geological facts

Pumice is the only rock that can float on water due to its incredible number of gas-filled vesicles. This specimen shows a weathered, rounded exterior typical of water transport.

Field identification & locations

Identify by its light weight and 'frothy' porous texture. It is commonly found in volcanic coastal regions or near active/dormant stratovolcanoes.

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