igneous

Pumice

Pumice (volcanic glass formed of highly vesicular rough textured rock)

Hardness: 5-6 Mohs (though very brittle); Color: ranges from white and cream to grey or green-tan; Luster: dull to silky; Structure: highly vesicular (full of gas bubbles), aphanitic; Specific Gravity: less than 1.0 (it floats on water).

Hardness: 5-6 Mohs (though very brittle)
Color: ranges from white and cream to grey or green-tan
Luster: dull to silky

Identified March 28, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles in a glass-like matrix. It can be found in volcanic regions of any geological age from the Cenozoic to the present.

Uses & applications

Used in construction (lightweight concrete/breezeblock), as an abrasive in skin exfoliation (pumice stones), in industrial polishing, and as an amendment in horticultural soil for drainage.

Geological facts

Pumice is the only rock that can float on water until it eventually becomes waterlogged. After the eruption of Krakatoa in 1883, rafts of pumice floated across the Indian Ocean for up to 20 years, with some supporting the growth of palm trees.

Field identification & locations

Identify in the field by its extreme lightness relative to size; it should feel almost like Styrofoam and often floats. Commonly found in volcanic areas like the Cascades (USA), Italy, and Iceland. Collectors look for pieces with unique colors or large vesicle structures.

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