igneous
Pumice (or Volcanic Scoria)
Vesicular Rhyolite or Vesicular Basalt
Hardness: 5-6 Mohs. Color: Grayish-white, cream, or reddish-brown. Luster: Dull. Structure: Highly vesicular (honeycombed with gas bubbles), fine-grained or glassy. Specific Gravity: Typically less than 1.0 (often floats in water).
- Hardness
- 5-6 Mohs
- Color
- Grayish-white, cream, or reddish-brown
- Luster
- Dull
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Physical properties
Hardness: 5-6 Mohs. Color: Grayish-white, cream, or reddish-brown. Luster: Dull. Structure: Highly vesicular (honeycombed with gas bubbles), fine-grained or glassy. Specific Gravity: Typically less than 1.0 (often floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles within the solidifying rock.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight concrete aggregate, and in landscaping or soil aeration.
Geological facts
Pumice is the only rock that can typically float on water until it becomes waterlogged. Massive rafts of floating pumice can travel across oceans for years after an eruption.
Field identification & locations
Identify in the field by its sponge-like appearance and extremely light weight relative to its size. Commonly found in volcanic regions like the Ring of Fire or near active/dormant volcanoes.
