Comparison · Igneous Rocks
Pumice vs Tuff
Pumice and Tuff are easy to confuse because both are igneous rocks. Pumice is harder (Mohs 5–6) than Tuff (Mohs 2–5), so Pumice will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Pumice and Tuff
- Pumice is harder (Mohs 5–6) than Tuff (Mohs 2–5), so Pumice will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
- Tuff feels noticeably heavier for its size (specific gravity 1.5–2.7 versus 0.25–0.9 for Pumice).
- Hold a thin edge to the light: Pumice is Opaque, translucent in thin shards, Tuff is Opaque.
- They overlap in white, gray, and brown, but Pumice also comes in yellow and Tuff also comes in pink and green.
Pumice vs Tuff properties
| Property | Pumice | Tuff |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 5–6 | 2–5 |
| Luster | Dull to glassy | Dull to earthy; glassy shards may show vitreous luster |
| Transparency | Opaque, translucent in thin shards | Opaque |
| Specific gravity | 0.25–0.9 | 1.5–2.7 |
| Crystal system | Amorphous | — |
| Common colors | White, Light gray, Tan, Pale yellow | Light gray, Tan, Pink, Greenish, White |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Pumice and Tuff trade in a similar range, around $10.
About Pumice
Pumice is a light-colored, extrusive volcanic rock so full of trapped gas bubbles, or vesicles, that it can float on water. It forms when gas-rich, silica-rich magma is violently depressurized during an explosive eruption, freezing the expanding bubbles in place as volcanic glass. Its extremely low density and rough, abrasive texture have made it useful to people for thousands of years.
About Tuff
Tuff is a volcanic rock formed from compacted and cemented volcanic ash ejected during explosive eruptions, distinguishing it from lava-derived rocks like basalt or andesite that solidify directly from molten flow. Its texture ranges from soft and crumbly to dense and welded, depending on how hot the ash was when it settled and how much compaction it underwent afterward. Tuff deposits can blanket enormous areas following a single major eruption, preserving a snapshot of that eruption's ash fall in the rock record.
Pumice vs Tuff FAQ
Is Pumice the same as Tuff?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Pumice is harder (Mohs 5–6) than Tuff (Mohs 2–5), so Pumice will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
How can you tell Pumice from Tuff?
Pumice is harder (Mohs 5–6) than Tuff (Mohs 2–5), so Pumice will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Tuff feels noticeably heavier for its size (specific gravity 1.5–2.7 versus 0.25–0.9 for Pumice). Hold a thin edge to the light: Pumice is Opaque, translucent in thin shards, Tuff is Opaque.
Which is harder, Pumice or Tuff?
Pumice is harder: Mohs 5–6 against Mohs 2–5 for Tuff.
Which is more valuable, Pumice or Tuff?
Typical specimens of Pumice and Tuff trade in a similar range, around $10.
