igneous

Pumice

Pumice (a highly vesicular amorphous volcanic glass)

Hardness: 5-6 (Mohs scale), Color: light gray to pale green/tan, Luster: vitreous to silky, Crystal structure: amorphous (none), Cleavage: none, Specific gravity: 0.25-1.2 (often floats in water), Porosity: highly vesicular.

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization cause gases to expand rapidly, creating a frothy, glass-like foam that solidifies. Can be found in volcanic regions of all ages, commonly Holocene.

Uses & applications

Used as an abrasive in soaps, pencil erasers, and stone-washed jeans. Also used in lightweight concrete, horticulture (soil aeration), and beauty products like pumice stones for skincare.

Geological facts

Pumice is the only rock that can reliably float on water for long periods. After massive volcanic eruptions, giant 'pumice rafts' can form in the ocean, drifting for thousands of miles and occasionally reaching heights of several feet thick.

Field identification & locations

Identify by its unusually light weight (low density) and frothy, sponge-like texture with numerous small holes (vesicles). It is commonly found near volcanic activity, especially near rhyolitic or dacitic vents.

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