Comparison · Materials vs Semi-Precious Stones
Glass vs Opal
Glass and Opal 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 Opal
- 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, Opal leaves white.
- They overlap in blue, but Glass also comes in green, brown, and clear and Opal also comes in white, black, and pink.
Glass vs Opal properties
| Property | Glass | Opal |
|---|---|---|
| Type | Materials | Semi-Precious Stones |
| Mohs hardness | 5.5 | 5.5 |
| Luster | vitreous | vitreous |
| Streak | White to colorless | White |
| Transparency | translucent | translucent |
| Specific gravity | 2.5 | 2.1 |
| Crystal system | amorphous | amorphous |
| Common colors | Green, Brown, Clear, Blue, White, Frosted | White, Black, Fire, Blue, Pink |
| Rarity | common | uncommon |
| Typical specimen value | $1–$40+ | $50–$10000+ |
Which is more valuable?
Opal is usually the more valuable of the two: a typical collector specimen runs about $500 against $5 for Glass, and premium Opal can reach $10000 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 Opal
Opal is famous for its play-of-color, caused by the diffraction of light through microscopic silica spheres. Australia produces 95% of the world's opals.
Glass vs Opal FAQ
Is Glass the same as Opal?
No. Glass is a material while Opal is a semi-precious stone. 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 Opal?
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, Opal leaves white. They overlap in blue, but Glass also comes in green, brown, and clear and Opal also comes in white, black, and pink.
Which is harder, Glass or Opal?
They are about equally hard, both near Mohs 5.5.
Which is more valuable, Glass or Opal?
Opal is usually the more valuable of the two: a typical collector specimen runs about $500 against $5 for Glass, and premium Opal can reach $10000 or more.
