igneous
Pumice
Pumice (Vesicular volcanic glass / Rhyolite or Trachyte)
Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: dull/pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: less than 1.0 (it floats in water).
- Hardness
- 5-6 (Mohs)
- Color
- white, cream, or light grey
- Luster
- dull/pearly
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Physical properties
Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: dull/pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: less than 1.0 (it floats in water).
Formation & geological history
Formed during explosive volcanic eruptions where highly pressurized lava rapidly cools and depressurizes, trapping gas bubbles within the rock material as it solidifies into glass.
Uses & applications
Used as an abrasive in hygiene products (exfoliating stones, toothpaste), in construction for lightweight concrete, and as a polishing agent for metal and wood.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that travel for thousands of miles across oceans.
Field identification & locations
Identify in the field by its extremely light weight and porous 'sponge-like' appearance. Commonly found near active or dormant volcanic regions like the Cascades, Mediterranean, or New Zealand.
