igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 (but very brittle); Color: Tan, beige, or grey; Luster: Dull to pearly; Structure: Amorphous/Vesicular; Specific Gravity: Often less than 1.0 (floats in water)
- Hardness
- 5-6 (but very brittle)
- Color
- Tan, beige, or grey
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 (but very brittle); Color: Tan, beige, or grey; Luster: Dull to pearly; Structure: Amorphous/Vesicular; Specific Gravity: Often less than 1.0 (floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when pressurized liquid rock is ejected into the air; rapid cooling and depressurization create bubbles (vesicles) as gases escape.
Uses & applications
Used in construction for lightweight concrete, as an abrasive in polishing and personal care (exfoliation), and in horticulture as a soil amendment.
Geological facts
Pumice is the only rock that can float on water due to its high porosity. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its extremely lightweight feel, rough sandpaper-like texture, and visible tiny holes. Commonly found in areas with past or present explosive volcanic activity.
