RocksdayPumice vs Volcanic Bomb
The quickest way to tell Pumice from Volcanic Bomb: Volcanic Bomb feels noticeably heavier for its size (specific gravity 2.2–3 vs 0.25–0.9).
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
A lump of lava larger than 64 mm that was still molten when it was thrown out, so it froze in a streamlined or cracked shape.
Photo: National Park Service/Ed Shiinoki, Public domain
Quick tests
- Heft: Volcanic Bomb feels noticeably heavier for its size (specific gravity 2.2–3 vs 0.25–0.9).
Key differences
- Pumice is pale and light enough to float.
Side by side
| Property | Pumice | Volcanic Bomb |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 5.5–6 | 5–6 |
| Luster | Dull to silky | Dull to glassy |
| Colors | White, Gray | Black, Brown, Red, Gray |
| Crystal system / structure | Vesicular (frothy) | Aerodynamic pyroclast |
| Specific gravity | 0.25–0.9 | 2.2–3 |
| Found in | Lipari, Italy; Santorini, Greece | Hawaii; Iceland |
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 volcanic bomb
- Almond, spindle or ribbon shape, or a round lump with a cracked crust.
- Often a dense core and a bubbly or breadcrust outside.
- Basaltic ones are black to reddish brown.
Structure: Aerodynamic pyroclast
Full Volcanic Bomb guide →More comparisons
Frequently asked questions
What is the difference between pumice and volcanic bomb?
Pumice is an igneous rock with a Mohs hardness of about 5.5–6 and a dull to silky luster, usually white or gray. Volcanic Bomb is an igneous rock with a Mohs hardness of about 5–6 and a dull to glassy luster, usually black, brown, red or gray.
How can you tell pumice from volcanic bomb?
Volcanic Bomb feels noticeably heavier for its size (specific gravity 2.2–3 vs 0.25–0.9). Pumice is pale and light enough to float.
Could you tell them apart from a blurry close-up?
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