igneous

Pumice

Pumice (Vesicular Rhyolite/Andesite)

Hardness: 5-6 Mohs; Color: Creamy white to light gray; Luster: Dull to pearly; Structure: Highly vesicular (honeycombed with air bubbles) and amorphous glass; Specific Gravity: 0.25-0.91 (floats in water).

Hardness: 5-6 Mohs
Color: Creamy white to light gray
Luster: Dull to pearly

Identified March 22, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles. Occurs in Cenozoic and younger volcanic arcs.

Uses & applications

Used as an abrasive in soaps (Lava soap), foot stones, and denim stone-washing; as a lightweight aggregate in concrete/cinder blocks; and as a soil amendment in horticulture for drainage.

Geological facts

Pumice is the only rock that consistently floats on water initially; massive 'pumice rafts' from underwater volcanoes can float across oceans for thousands of miles.

Field identification & locations

Identify in the field by its extreme lightness (low density) and frothy, sponge-like texture. Common in volcanic regions such as the Cascades (USA), Italy, Greece, and New Zealand.

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