igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 (but brittle/crumbly); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.70 (floats in water).

Hardness: 5-6 (but brittle/crumbly)
Color: White, cream, or light grey
Luster: Dull to pearly

Identified May 29, 2026More igneous →

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Physical properties

Hardness: 5-6 (but brittle/crumbly); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.70 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected and cools rapidly, trapping gas bubbles in a frothy glass matrix.

Uses & applications

Used as an abrasive in soaps (Lava soap), foot stones for skin exfoliation, dental polishing, lightweight concrete aggregate, and stone-washing textiles like denim.

Geological facts

Pumice is the only rock that consistently floats on water due to its air-filled pores. After major eruptions, vast 'pumice rafts' can form in the ocean, drifting for thousands of miles.

Field identification & locations

Identify in the field by its extremely light weight, frothy 'sponge-like' appearance, and ability to float. Commonly found in volcanic regions like the Andes, Cascades, or Mediterranean.

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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