Comparison · Igneous Rocks
Andesite vs Obsidian
Andesite and Obsidian 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 Obsidian
- Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Hold a thin edge to the light: Andesite is Opaque, Obsidian is translucent.
- They overlap in green, brown, and black, but Andesite also comes in gray and Obsidian also comes in multicolored.
Andesite vs Obsidian properties
| Property | Andesite | Obsidian |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 5–6 | 5.5 |
| Luster | Dull groundmass with vitreous phenocrysts | vitreous |
| Streak | — | White |
| Transparency | Opaque | translucent |
| Specific gravity | 2.5–2.8 | 2.4 |
| Crystal system | — | amorphous |
| Common colors | Gray, Dark gray, Greenish gray, Brown, Black | Black, Brown, Green, Rainbow |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $5–$100+ |
Which is more valuable?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Andesite, and premium Obsidian can reach $100 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 Obsidian
Obsidian is a naturally occurring volcanic glass formed from rapidly cooled lava. Its sharp edges made it invaluable for ancient tools and weapons.
Andesite vs Obsidian FAQ
Is Andesite the same as Obsidian?
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 Obsidian?
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hold a thin edge to the light: Andesite is Opaque, Obsidian is translucent. They overlap in green, brown, and black, but Andesite also comes in gray and Obsidian also comes in multicolored.
Which is harder, Andesite or Obsidian?
They are about equally hard, both near Mohs 5–6.
Which is more valuable, Andesite or Obsidian?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Andesite, and premium Obsidian can reach $100 or more.
