Igneous

Pumice

Pumicite (Amorphous volcanic glass)

Hardness: 5-6 Mohs. Color: Light gray, tan, or yellowish. Luster: Dull to pearly. Texture: Highly vesicular (honeycombed with air bubbles). Specific Gravity: Often less than 1.0 (floats in water).

Hardness: 5-6 Mohs
Color: Light gray, tan, or yellowish
Luster: Dull to pearly

Identified March 5, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs. Color: Light gray, tan, or yellowish. Luster: Dull to pearly. Texture: Highly vesicular (honeycombed with air bubbles). Specific Gravity: Often less than 1.0 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich frothy magma is ejected and cools rapidly, trapping gas bubbles. Common in Quaternary volcanic deposits.

Uses & applications

Used as an abrasive in cosmetics (exfoliants), hygiene (pumice stones), metal polishing, construction (lightweight concrete), and as a soil amendment in horticulture.

Geological facts

Pumice is the only rock known to humans that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that drift across oceans for years.

Field identification & locations

Identify by its extremely lightweight feel and visible porous texture. Commonly found in vicinity of volcanoes with silicic lava. To test in the field, see if it floats in a body of water.

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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