igneous

Pumice

Vesicular volcanic glass (Amorphous silica mixed with various oxides)

Hardness: 5-6 Mohs; Color: Light gray, tan, or cream; Luster: Vitreous to dull; Structure: Highly vesicular/porous; Crystal Structure: Amorphous (glassy); Specific Gravity: 0.25-0.9 (floats in water).

Hardness: 5-6 Mohs
Color: Light gray, tan, or cream
Luster: Vitreous to dull

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 into the atmosphere. Rapid cooling and depressurization create bubbles (vesicles) trapped in solidifying glass.

Uses & applications

Used as an abrasive in soaps, toothpastes, and heavy-duty cleaners. Extensively used in horticulture as a soil amendment, in construction for lightweight concrete, and in garment manufacturing for stonewashing denim.

Geological facts

Pumice is the only rock that can float on water due to its incredible porosity. Massive 'pumice rafts' have been known to float across oceans for years following major volcanic eruptions.

Field identification & locations

Identify in the field by its sponge-like appearance and extremely light weight. If it floats in a puddle or stream, it is likely pumice or scoria (though scoria usually sinks). Found in volcanic regions like the Cascades (USA), Italy, and Iceland.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral