Comparison · Igneous Rocks
Ignimbrite vs Pumice
Ignimbrite and Pumice are easy to confuse because both are igneous rocks. Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Ignimbrite and Pumice
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Ignimbrite is dull while Pumice is dull to glassy.
- Ignimbrite feels noticeably heavier for its size (specific gravity 2.25 versus 0.25–0.9 for Pumice).
- Hold a thin edge to the light: Ignimbrite is opaque, Pumice is Opaque, translucent in thin shards.
- They overlap in brown, gray, and white, but Ignimbrite also comes in pink, red, and black and Pumice also comes in yellow.
Ignimbrite vs Pumice properties
| Property | Ignimbrite | Pumice |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 6 | 5–6 |
| Luster | dull | Dull to glassy |
| Streak | Variable; often light gray or tan | — |
| Transparency | opaque | Opaque, translucent in thin shards |
| Specific gravity | 2.25 | 0.25–0.9 |
| Crystal system | varies | Amorphous |
| Common colors | Tan, Pink, Gray, White, Red brown, Black | White, Light gray, Tan, Pale yellow |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Ignimbrite and Pumice trade in a similar range, around $10.
About Ignimbrite
Ignimbrite is a volcanic rock formed from hot pyroclastic flows. It can look like tuff with pumice fragments, ash, crystals, and sometimes flattened streaks from welding.
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.
Ignimbrite vs Pumice FAQ
Is Ignimbrite the same as Pumice?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Ignimbrite from Pumice?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Ignimbrite is dull while Pumice is dull to glassy. Ignimbrite feels noticeably heavier for its size (specific gravity 2.25 versus 0.25–0.9 for Pumice).
Which is harder, Ignimbrite or Pumice?
Ignimbrite is harder: Mohs 6 against Mohs 5–6 for Pumice.
Which is more valuable, Ignimbrite or Pumice?
Typical specimens of Ignimbrite and Pumice trade in a similar range, around $10.
