igneous

Pumice

Vesicular Rhyolite or Dacite Pumice (Amorphous volcanic glass)

Hardness: 5-6 Mohs (though brittle and easy to crush); Color: light gray, tan, or cream; Luster: dull to pearly; Structure: highly vesicular (pitted with gas bubbles); Specific Gravity: 0.25 to 0.70 (will often float in water).

Hardness: 5-6 Mohs (though brittle and easy to crush)
Color: light gray, tan, or cream
Luster: dull to pearly

Identified March 19, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when magma with high water and gas content is depressurized. The rapid cooling traps gas bubbles, creating a solidified froth. Commonly found in young volcanic belts (Cenozoic to modern age).

Uses & applications

Used as an abrasive in cosmetics (exfoliants), household cleaners, and stonewashed jeans. In construction, it is used as a lightweight aggregate for concrete and as horticultural soil amendment.

Geological facts

Pumice is the only rock that can float on water until it eventually becomes water-logged. Large eruptions can create 'pumice rafts' in the ocean that are hundreds of miles long and can drift for years.

Field identification & locations

Identify by its extremely lightweight feel, abrasive texture, and presence of tiny voids. Found in volcanic regions like the Cascades, Andes, or Mediterranean. Collect from dry wash beds or volcanic ash deposits.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral