igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 (Mohs); Color: Light gray to cream; Luster: Dull to pearly; Structure: Vesicular (highly porous/frothy); Specific Gravity: 0.25-0.9 (floats in water).

Hardness: 5-6 (Mohs)
Color: Light gray to cream
Luster: Dull to pearly

Identified April 9, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Light gray to cream; Luster: Dull to pearly; Structure: Vesicular (highly porous/frothy); Specific Gravity: 0.25-0.9 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping air bubbles in the solidifying glass. Found in areas with geologically recent volcanic activity.

Uses & applications

Used as an abrasive in soaps, foot stones, and industrial polishing; lightweight aggregate in concrete; horticultural soil amendment; and in stone-washing textiles like blue jeans.

Geological facts

Pumice is the only rock that can reliably float on water because of its low density and air-trapped vesicles. Huge rafts of floating pumice can occasionally be seen in the ocean following submarine eruptions.

Field identification & locations

Identified by its extremely lightweight feel, light color, and porous, sponge-like texture. If it floats in water, it is almost certainly pumice or a related volcanic glass.

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