igneous

Pumice

Pumicite (Amorphous Volcanic Glass)

Hardness: 5-6 (Mohs scale), Color: light gray to cream, Luster: dull to pearly (silky), Structure: highly vesicular (pitted with air bubbles), Specific Gravity: very low (less than 1.0, floats in water).

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when magma with high gas and water content is ejected into the air; it cools rapidly (quenching) while gases expand to create a frothy texture.

Uses & applications

Used as an abrasive in polishing and liquid soaps, as a lightweight aggregate for concrete and cinder blocks, in horticulture as a soil conditioner, and for exfoliating skin (pumice stones).

Geological facts

Pumice is the only rock that can float on water due to its trapped air bubbles. Large underwater eruptions can create 'pumice rafts' that drift for thousands of miles across the ocean.

Field identification & locations

Identify by its light-as-air weight and porous 'sponge-like' appearance. Commonly found in volcanic regions such as the Ring of Fire, Mediterranean islands, and the Andes. If it floats in a glass of water, it is almost certainly pumice.

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