igneous

Pumice

Vesicular volcanic glass

Hardness: 5-6 Mohs. Color: White, cream, or light grey. Luster: Vitreous to dull. Structure: Vesicular (highly porous) and amorphous (glassy). Cleavage: None. Specific gravity: 0.25 to 0.7 (floats in water).

Hardness: 5-6 Mohs
Color: White, cream, or light grey
Luster: Vitreous to dull

Identified March 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when volatile-rich silicic magma cools rapidly, trapping gas bubbles. Ages range from Holocene to millions of years depending on local volcanic activity.

Uses & applications

Used as an abrasive in polishing, exfoliating soaps, and beauty products. In construction, it is used as a lightweight aggregate for concrete and as a landscaping stone. It is also used in stonewashed denim production.

Geological facts

Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large outbreaks of pumice in the ocean are known as 'pumice rafts' and can travel thousands of miles.

Field identification & locations

Identify in the field by its sponge-like appearance and its incredibly light weight compared to its size. Often found in proximity to volcanic regions like the Ring of Fire or Iceland. If it floats, it is likely pumice.

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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