Comparison · Igneous Rocks
Obsidian vs Rhyolite
Obsidian and Rhyolite are easy to confuse because both are igneous rocks. Both sit near Mohs 5.5, 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 Obsidian and Rhyolite
- Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Hold a thin edge to the light: Obsidian is translucent, Rhyolite is Opaque.
- They overlap in brown and multicolored, but Obsidian also comes in black and green and Rhyolite also comes in pink, gray, red, and white.
Obsidian vs Rhyolite properties
| Property | Obsidian | Rhyolite |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 5.5 | 5.5–7 |
| Luster | vitreous | Dull to vitreous (glassy groundmass) |
| Streak | White | — |
| Transparency | translucent | Opaque |
| Specific gravity | 2.4 | 2.35–2.7 |
| Crystal system | amorphous | — |
| Common colors | Black, Brown, Green, Rainbow | Pink, Gray, Tan, Red, White, Banded |
| Rarity | common | common |
| Typical specimen value | $5–$100+ | $1–$75+ |
Which is more valuable?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rhyolite, and premium Obsidian can reach $100 or more.
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.
About Rhyolite
Rhyolite is a fine-grained volcanic igneous rock chemically equivalent to granite but formed by rapid cooling of silica-rich lava at or near Earth's surface rather than slow crystallization underground. Its high silica content makes rhyolitic magma extremely viscous, often producing explosive eruptions and distinctive flow-banded textures as the sticky lava moves sluggishly before solidifying. Rhyolite typically appears pale gray, pink, or tan and frequently contains visible bands or streaks recording its flow history.
Obsidian vs Rhyolite FAQ
Is Obsidian the same as Rhyolite?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Obsidian from Rhyolite?
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hold a thin edge to the light: Obsidian is translucent, Rhyolite is Opaque. They overlap in brown and multicolored, but Obsidian also comes in black and green and Rhyolite also comes in pink, gray, red, and white.
Which is harder, Obsidian or Rhyolite?
Rhyolite is harder: Mohs 5.5–7 against Mohs 5.5 for Obsidian.
Which is more valuable, Obsidian or Rhyolite?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rhyolite, and premium Obsidian can reach $100 or more.
