igneous
Pumice
Pumice (Vesicular Rhyolite/Dacite)
Hardness: 5-6 (Mohs scale), though very brittle. Color: Cream, white, or light gray. Luster: Dull to pearly. Structure: Highly vesicular (foamy) texture with microscopic pores. Specific Gravity: 0.25 to 0.9 depending on porosity; will float on water.
- Hardness
- 5-6 (Mohs scale), though very brittle
- Color
- Cream, white, or light gray
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 (Mohs scale), though very brittle. Color: Cream, white, or light gray. Luster: Dull to pearly. Structure: Highly vesicular (foamy) texture with microscopic pores. Specific Gravity: 0.25 to 0.9 depending on porosity; will float on water.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected into the atmosphere. The rapid cooling and depressurization trap gas bubbles in a glass-like matrix. Environments: Volcanic arcs and explosive vents.
Uses & applications
Used as an abrasive in polishing, exfoliating soaps, and stonewashed denim production. In construction, it is used as a lightweight aggregate for concrete and as a landscaping stone. Also used in horticulture to aerate soil.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice can drift across oceans for years following massive submarine or island eruptions.
Field identification & locations
Identify in the field by its extreme lightness and rough, scratchy texture. It is often found in volcanic ash deposits or near the sites of pyroclastic flows. Common locations include the Cascades (USA), Italy, Greece, and Iceland.
