RocksdayPumice vs Tuff
How to tell them apart
Volcanic glass so full of gas bubbles that it floats on water. It forms in explosive, gas-rich eruptions.
Photo: User MPF on en.wikipedia, CC BY-SA 3.0
Rock made of compacted volcanic ash, often soft enough to carve.
Photo: Ivan Fernanadez 1011, CC BY-SA 4.0
Quick tests
- Hardness: Pumice is clearly harder: Mohs 5.5–6 versus 3–5.
- Heft: Tuff feels noticeably heavier for its size (specific gravity 1.5–2.5 vs 0.25–0.9).
Key differences
- Pumice is frothy glass that floats.
Side by side
| Property | Pumice | Tuff |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 5.5–6 | 3–5 |
| Luster | Dull to silky | Dull |
| Colors | White, Gray | White, Gray, Pink, Brown |
| Crystal system / structure | Vesicular (frothy) | Pyroclastic (volcanic ash) |
| Specific gravity | 0.25–0.9 | 1.5–2.5 |
| Found in | Lipari, Italy; Santorini, Greece | Cappadocia, Turkey; Rapa Nui (Easter Island) |
Properties that are the same for both are grayed out.
How to identify pumice
- Very light — it floats.
- Pale gray or white.
- Full of tiny bubbles and stretched fibers.
- Feels rough and scratchy.
Structure: Vesicular (frothy)
Full Pumice guide →How to identify tuff
- Light, porous and often crumbly.
- Gritty with fragments of pumice, crystals and rock.
- Pale colors; may show layering.
Structure: Pyroclastic (volcanic ash)
Full Tuff guide →More comparisons
Could you tell them apart from a blurry close-up?
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