igneous
Pumice and Scoria
Vesicular Volcanic Rock (Pumice: Silicic / Scoria: Mafic)
Hardness: 5-6 Mohs; Color: Pale white/cream (Pumice) and Reddish-brown (Scoria); Luster: Dull/Earthy; Texture: Highly vesicular (pitted with gas bubbles); Specific Gravity: Pumice is often < 1.0 (floats), Scoria > 1.0 (sinks).
- Hardness
- 5-6 Mohs
- Color
- Pale white/cream (Pumice) and Reddish-brown (Scoria)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 Mohs; Color: Pale white/cream (Pumice) and Reddish-brown (Scoria); Luster: Dull/Earthy; Texture: Highly vesicular (pitted with gas bubbles); Specific Gravity: Pumice is often < 1.0 (floats), Scoria > 1.0 (sinks).
Formation & geological history
Extrusive igneous rocks formed during explosive volcanic eruptions. Pumice forms from gas-rich silicic lava cooling rapidly, while Scoria forms from darker, iron-rich basaltic/andesitic lava.
Uses & applications
Abrasives in soaps and beauty products (pumice stones), lightweight aggregate in concrete, landscaping (lava rock), and filtration media.
Geological facts
Pumice is the only rock that can float on water due to its extreme porosity. Scoria is often used as the 'lava rock' found in gas grills and garden beds.
Field identification & locations
Identified by their lightweight, sponge-like appearance and many visible pores (vesicles). Found in volcanic regions like Iceland, Italy, and the Pacific Northwest.
