igneous
Pumice
Pumice (Vesicular Felsic Igneous Rock)
Hardness: 6 on the Mohs scale; Color: Light gray, white, yellowish, or tan; Luster: Dull to earthy; Crystal Structure: Amorphous (volcanic glass with a frothy texture); Cleavage: None; Specific Gravity: Less than 1.0 (it floats on water due to numerous gas bubbles).
- Hardness
- 6 on the Mohs scale
- Color
- Light gray, white, yellowish, or tan
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on the Mohs scale; Color: Light gray, white, yellowish, or tan; Luster: Dull to earthy; Crystal Structure: Amorphous (volcanic glass with a frothy texture); Cleavage: None; Specific Gravity: Less than 1.0 (it floats on water due to numerous gas bubbles).
Formation & geological history
Formed from explosive volcanic eruptions where felsic lava containing high amounts of gas and water is rapidly cooled and depressurized, trapping gas bubbles within the glassy matrix.
Uses & applications
Used widely in lightweight construction aggregates, abrasives (such as in pumice stone for personal care, stone-washing jeans, and eraser rubbers), horticulture as a soil conditioner, and filtration media.
Geological facts
Pumice is one of the only rocks that can float on water. When catastrophic volcanic eruptions occur, massive floating rafts of pumice can drift across oceans for months.
Field identification & locations
Easily identifiable in the field by its very light weight, pale color, and vesicular (sponge-like, bubbly) texture. Commonly found near active or past volcanic regions globally, particularly around subduction zones.
