igneous
Pumice and Scoria
Vesicular Volcanic Ejecta (Rhyolite/Andesite/Basalt)
Hardness: 5-6 (Mohs); Color: Light gray to white (pumice) and dark red to black (scoria); Luster: Dull to earthy; Structure: Highly vesicular/porous; Specific Gravity: Below 1.0 (pumice often floats) to 2.5.
- Hardness
- 5-6 (Mohs)
- Color
- Light gray to white (pumice) and dark red to black (scoria)
- Luster
- Dull to earthy
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Light gray to white (pumice) and dark red to black (scoria); Luster: Dull to earthy; Structure: Highly vesicular/porous; Specific Gravity: Below 1.0 (pumice often floats) to 2.5.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) is ejected. Rapid cooling traps gas bubbles, creating a sponge-like texture. Commonly found in Quaternary volcanic deposits.
Uses & applications
Used as an abrasive in soaps (pumice), in lightweight concrete, as landscaping stone (lava rock), and for stone-washing denim. Pumice is also used in skin exfoliation products.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Massive 'pumice rafts' have been observed in the ocean following underwater volcanic eruptions.
Field identification & locations
Identify by the extreme lightness and pore-filled texture. If it feels much lighter than its size suggests and has a scratchy, 'foamy' surface, it is likely pumice or scoria. Found near active or dormant volcanoes worldwide.
