Comparison · Igneous Rocks
Andesite vs Basalt
Andesite and Basalt are easy to confuse because both are igneous rocks. Both sit near Mohs 5–6, 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 Andesite and Basalt
- Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Andesite is dull groundmass with vitreous phenocrysts while Basalt is dull.
- Hold a thin edge to the light: Andesite is Opaque, Basalt is opaque.
- They overlap in gray, green, and black, but Andesite also comes in brown.
Andesite vs Basalt properties
| Property | Andesite | Basalt |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 5–6 | 6 |
| Luster | Dull groundmass with vitreous phenocrysts | dull |
| Streak | — | Variable; test individual minerals |
| Transparency | Opaque | opaque |
| Specific gravity | 2.5–2.8 | 3 |
| Crystal system | — | varies |
| Common colors | Gray, Dark gray, Greenish gray, Brown, Black | Black, Dark Gray, Dark Green |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$30+ |
Which is more valuable?
Andesite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Andesite can reach $75 or more.
About Andesite
Andesite is a fine-grained, intermediate volcanic rock formed from lava with a silica content between basalt and rhyolite, typically 57 to 63 percent. It is named for the Andes Mountains, where it makes up much of the volcanic arc, and its groundmass is usually too fine to identify individual minerals without magnification. Andesite forms at convergent plate boundaries where oceanic crust melts beneath continental or island arcs.
About Basalt
Basalt is a dark, fine-grained volcanic rock that makes up most of the ocean floor and Hawaiian Islands. It often forms distinctive columnar jointing.
Andesite vs Basalt FAQ
Is Andesite the same as Basalt?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Andesite from Basalt?
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Andesite is dull groundmass with vitreous phenocrysts while Basalt is dull. Hold a thin edge to the light: Andesite is Opaque, Basalt is opaque.
Which is harder, Andesite or Basalt?
Basalt is harder: Mohs 6 against Mohs 5–6 for Andesite.
Which is more valuable, Andesite or Basalt?
Andesite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Andesite can reach $75 or more.
