igneous
Pumice
Pumice (Felsic volcanic rock)
Hardness: 5-6 Mohs. Color: White, light gray, or tan. Luster: Dull to pearly. Structure: Highly vesicular (porous) with many tiny holes. Specific gravity: Extremely low (often floats on water).
- Hardness
- 5-6 Mohs
- Color
- White, light gray, or tan
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs. Color: White, light gray, or tan. Luster: Dull to pearly. Structure: Highly vesicular (porous) with many tiny holes. Specific gravity: Extremely low (often floats on water).
Formation & geological history
Formed during explosive volcanic eruptions where highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles as the rock solidifies.
Uses & applications
Used as an abrasive in skincare (pumice stones), heavy-duty cleaning, concrete additives, pencil erasers, and as a growing medium in horticulture.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice have been known to drift across oceans for years after eruptions.
Field identification & locations
Identify by its light weight and 'frothy' appearance with visible vesicles (gas bubbles). It feels rough and scratchy. Found in volcanic regions like the Cascades, Italy, or Iceland.
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