igneous

Pumice (Volcanic Rock)

Vesicular volcanic rock (composed largely of amorphous volcanic glass)

Hardness: 5-6 (but very brittle); Color: Grey, white, or cream; Luster: Dull/Glassy; Structure: Vesicular (pitted with air bubbles); Specific Gravity: Sub-1.0 (floats in water).

Hardness: 5-6 (but very brittle)
Color: Grey, white, or cream
Luster: Dull/Glassy

Identified April 5, 2026More igneous →

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Physical properties

Hardness: 5-6 (but very brittle); Color: Grey, white, or cream; Luster: Dull/Glassy; Structure: Vesicular (pitted with air bubbles); Specific Gravity: Sub-1.0 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles in a solidified glass foam.

Uses & applications

Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight concrete additives, and horticultural soil drainage.

Geological facts

Pumice is the only rock that can float on water for long periods when dry. Large accumulations in the ocean are known as 'pumice rafts' and can drift for thousands of miles.

Field identification & locations

Identify by its extremely lightweight feel (low density) and the presence of numerous small holes (vesicles). Found in volcanic regions like the American West, Iceland, and Italy.

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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)

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Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

mineral