Comparison · Materials vs Igneous Rocks
Glass vs Obsidian
Glass and Obsidian are easy to confuse. 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 Glass and Obsidian
- Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Glass leaves a white to colorless streak on unglazed porcelain, Obsidian leaves white.
- They overlap in green and brown, but Glass also comes in clear and blue and Obsidian also comes in black and multicolored.
Glass vs Obsidian properties
| Property | Glass | Obsidian |
|---|---|---|
| Type | Materials | Igneous Rocks |
| Mohs hardness | 5.5 | 5.5 |
| Luster | vitreous | vitreous |
| Streak | White to colorless | White |
| Transparency | translucent | translucent |
| Specific gravity | 2.5 | 2.4 |
| Crystal system | amorphous | amorphous |
| Common colors | Green, Brown, Clear, Blue, White, Frosted | Black, Brown, Green, Rainbow |
| Rarity | common | common |
| Typical specimen value | $1–$40+ | $5–$100+ |
Which is more valuable?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $5 for Glass, and premium Obsidian can reach $100 or more.
About Glass
Glass is a man-made amorphous material. Surf-tumbled sea glass and weathered bottle shards are among the most common glassy finds mistaken for natural minerals.
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.
Glass vs Obsidian FAQ
Is Glass the same as Obsidian?
No. Glass is a material while Obsidian is a igneous rock. 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 Glass from Obsidian?
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Glass leaves a white to colorless streak on unglazed porcelain, Obsidian leaves white. They overlap in green and brown, but Glass also comes in clear and blue and Obsidian also comes in black and multicolored.
Which is harder, Glass or Obsidian?
They are about equally hard, both near Mohs 5.5.
Which is more valuable, Glass or Obsidian?
Obsidian is usually the more valuable of the two: a typical collector specimen runs about $20 against $5 for Glass, and premium Obsidian can reach $100 or more.
