igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 (Mohs), though brittle; Color: white, cream, or light grey; Luster: dull to pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: 0.25 to 0.9 (floats in water).

Hardness: 5-6 (Mohs), though brittle
Color: white, cream, or light grey
Luster: dull to pearly

Identified March 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when pressurized, gas-rich molten rock (magma) is ejected into the air, cools rapidly, and depressurizes, freezing the gas bubbles inside a glass matrix.

Uses & applications

Used as an abrasive in cleaning products, exfoliating stones for personal care (pumice stones), lightweight aggregate in concrete/cinder blocks, and in stonewashing textiles like denim jeans.

Geological facts

Pumice is the only rock that can float on water until it becomes waterlogged. Massive 'pumice rafts' resulting from underwater eruptions have been known to float across oceans for years.

Field identification & locations

Identify in the field by its extreme lightness (low density) and frothy, abrasive texture. Commonly found in volcanic regions such as the Ring of Fire or areas with history of rhyolitic eruptions.

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