igneous

Pumice

Pumice (a highly vesicular extrusive volcanic rock)

Hardness: 5-6 (Mohs scale), Color: light grey to cream, Luster: dull to silky, Structure: highly vesicular/frothy (amorphous volcanic glass), Specific Gravity: 0.25-0.9 (floats in water)

Identified May 23, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 5-6 (Mohs scale), Color: light grey to cream, Luster: dull to silky, Structure: highly vesicular/frothy (amorphous volcanic glass), Specific Gravity: 0.25-0.9 (floats in water)

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected rapidly. The sudden drop in pressure causes dissolved gases to expand into bubbles (vesicles) as the lava cools almost instantly. It is found in volcanic arcs and continental volcanic fields.

Uses & applications

Used as an abrasive in soaps (pumice stone), cosmetics, and toothpastes. In construction, it is used as a lightweight aggregate for concrete and cinder blocks. It is also used in horticulture for soil aeration.

Geological facts

Pumice is the only rock that can float on water due to its extreme porosity. During massive volcanic eruptions, 'pumice rafts' can form on the ocean that are miles long and can float for years.

Field identification & locations

Identify by its extremely lightweight feel; it will feel much lighter than it looks. It is commonly found in areas of past or present explosive volcanic activity like the Cascade Range in the US, Italy, or Iceland.

Other igneous specimens

See all

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