Igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 Mohs scale; Color: Cream, white, or light gray; Luster: Pearly or dull; Structure: Highly vesicular/porous; Cleavage: None; Specific gravity: 0.25 to 0.9 (often floats on water).
- Hardness
- 5-6 Mohs scale
- Color
- Cream, white, or light gray
- Luster
- Pearly or dull
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Physical properties
Hardness: 5-6 Mohs scale; Color: Cream, white, or light gray; Luster: Pearly or dull; Structure: Highly vesicular/porous; Cleavage: None; Specific gravity: 0.25 to 0.9 (often floats on water).
Formation & geological history
Formed through explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization cause gases to expand rapidly, creating a frothy, glass-rich mass. Can be found in volcanic deposits of any age, particularly from Cenozoic to recent eras.
Uses & applications
Commonly used as an abrasive in cleaning products (pumice stones), cosmetic exfoliants, and heavy-duty soaps. In construction, it is used as a lightweight aggregate for concrete and as a landscaping decoration.
Geological facts
Pumice is the only rock known to man that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that drift across oceans for thousands of miles.
Field identification & locations
Identify in the field by its extreme lightness relative to its size and its rough, sandpaper-like texture. Found in areas of past or present explosive volcanic activity like the Ring of Fire or Iceland. Collectors should look for uniform vesicular structure and low density.
