Comparison · Tektites vs Materials
Moldavite vs Slag Glass
Moldavite and Slag Glass 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 Moldavite and Slag Glass
- 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: Moldavite leaves a white streak on unglazed porcelain, Slag Glass leaves white to colorless.
- They overlap in green, but Slag Glass also comes in blue, black, brown, and white.
Moldavite vs Slag Glass properties
| Property | Moldavite | Slag Glass |
|---|---|---|
| Type | Tektites | Materials |
| Mohs hardness | 5.5 | 5.5 |
| Luster | vitreous | vitreous |
| Streak | White | White to colorless |
| Transparency | translucent | translucent |
| Specific gravity | 2.4 | 2.5 |
| Crystal system | amorphous | amorphous |
| Common colors | Forest Green, Olive Green | Blue, Green, Black, Brown, White, Swirled |
| Rarity | rare | common |
| Typical specimen value | $50–$2000+ | $1–$80+ |
Which is more valuable?
Moldavite is usually the more valuable of the two: a typical collector specimen runs about $200 against $10 for Slag Glass, and premium Moldavite can reach $2000 or more.
About Moldavite
Moldavite is a green tektite formed by a meteorite impact about 15 million years ago. Found only in the Czech Republic, it's prized by collectors and crystal enthusiasts.
About Slag Glass
Slag Glass is glassy industrial byproduct or manufactured glass with swirled colors, sometimes collected or knapped like stone.
Moldavite vs Slag Glass FAQ
Is Moldavite the same as Slag Glass?
No. Moldavite is a tektite while Slag Glass is a material. 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 Moldavite from Slag Glass?
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: Moldavite leaves a white streak on unglazed porcelain, Slag Glass leaves white to colorless. They overlap in green, but Slag Glass also comes in blue, black, brown, and white.
Which is harder, Moldavite or Slag Glass?
They are about equally hard, both near Mohs 5.5.
Which is more valuable, Moldavite or Slag Glass?
Moldavite is usually the more valuable of the two: a typical collector specimen runs about $200 against $10 for Slag Glass, and premium Moldavite can reach $2000 or more.
