igneous
Pumice
Volcanic glass / Pumice
Hardness: 6 on Mohs scale (for the glass framework, though bulk rock is easily crushed); Color: White, yellowish, grey, or light brown; Luster: Earthy to silky; Crystal structure: Amorphous (glassy); Specific gravity: Less than 1.0 (floats on water).
- Color
- White, yellowish, grey, or light brown
- Luster
- Earthy to silky
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale (for the glass framework, though bulk rock is easily crushed); Color: White, yellowish, grey, or light brown; Luster: Earthy to silky; Crystal structure: Amorphous (glassy); Specific gravity: Less than 1.0 (floats on water).
Formation & geological history
Formed from explosive volcanic eruptions where felsic or intermediate lava with high gas content is ejected into the air, depressurizing rapidly and cooling so quickly that gas bubbles are trapped as the lava solidifies into foam.
Uses & applications
Used in lightweight concrete, abrasives (pumice stone for personal care, scrubbing, and polishing), horticulture as a soil amendment, and filtration media.
Geological facts
Pumice is one of the only naturally occurring stones that can float on water due to its extremely high porosity, formed by expanding gases escaping solidifying lava.
Field identification & locations
Easily identified by its extremely light weight, pale color, abrasive texture, and high density of tiny air bubble holes (vesicles). Commonly found near young volcanic regions worldwide.
