igneous
Pumice
Pumice (Volcanic Rock)
Hardness: 6 on Mohs scale (due to the glass framework, though the bulk rock feels fragile). Color: Light gray, white, yellowish, or brownish. Luster: Dull to earthy. Crystal structure: Amorphous, highly vesicular glassy volcanic rock. Specific gravity: Extremely low, often less than 1.0, allowing it to float on water.
- Color
- Light gray, white, yellowish, or brownish
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on Mohs scale (due to the glass framework, though the bulk rock feels fragile). Color: Light gray, white, yellowish, or brownish. Luster: Dull to earthy. Crystal structure: Amorphous, highly vesicular glassy volcanic rock. Specific gravity: Extremely low, often less than 1.0, allowing it to float on water.
Formation & geological history
Formed from explosive volcanic eruptions where gas-rich, felsic to intermediate lava rapidly cools and depressurizes, trapping gas bubbles (vesicles) within the glassy matrix. Found globally in regions with recent or ancient volcanic activity.
Uses & applications
Widely used in lightweight construction aggregates, concrete manufacture, abrasive soaps, horticultural soil conditioning, and personal care products like pumice stones for skin exfoliation.
Geological facts
Pumice is one of the only rocks known to float on water due to its high porosity and trapped air chambers. It has been used historically by the ancient Romans as a lightweight building material and abrasive.
Field identification & locations
Easily identified by its extremely light weight, pale color, rough texture, and abundance of small holes or vesicles. Common in volcanic arcs and convergent plate boundaries worldwide.
