Comparison · Minerals vs Precious Stones
Corundum vs Sapphire
Corundum and Sapphire are easy to confuse. Both sit near Mohs 9, 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 Corundum and Sapphire
- Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Sapphire leaves white.
- Hold a thin edge to the light: Corundum is Transparent to translucent, Sapphire is transparent.
- They overlap in blue, yellow, green, and pink, but Corundum also comes in red, clear, and gray and Sapphire also comes in orange and white.
- Well-formed crystals give it away: Corundum is Trigonal, Sapphire is trigonal.
Corundum vs Sapphire properties
| Property | Corundum | Sapphire |
|---|---|---|
| Type | Minerals | Precious Stones |
| Mohs hardness | 9 | 9 |
| Luster | Adamantine to vitreous | adamantine |
| Streak | White (colorless) | White |
| Transparency | Transparent to translucent | transparent |
| Specific gravity | 3.95–4.10 | 4 |
| Crystal system | Trigonal | trigonal |
| Common colors | Red (ruby), Blue (sapphire), Colorless, Yellow, Green, Pink, Gray | Blue, Pink, Yellow, Orange, Green, White |
| Rarity | common | rare |
| Typical specimen value | $2–$150+ | $500–$50000+ |
Which is more valuable?
Sapphire is usually the more valuable of the two: a typical collector specimen runs about $5000 against $20 for Corundum, and premium Sapphire can reach $50000 or more.
About Corundum
Corundum is aluminum oxide, Al2O3, crystallizing in the trigonal system and ranking as the second-hardest natural mineral after diamond. Its gem varieties, red ruby and every other color of sapphire, are colored by trace amounts of chromium, iron, or titanium substituting into an otherwise colorless crystal structure. Non-gem corundum is widely used as an industrial abrasive under the name emery.
About Sapphire
Sapphire is a variety of corundum in any color except red. Blue sapphires are most prized, especially the legendary Kashmir stones.
Corundum vs Sapphire FAQ
Is Corundum the same as Sapphire?
No. Corundum is a mineral while Sapphire is a precious stone. Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Corundum from Sapphire?
Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Sapphire leaves white. Hold a thin edge to the light: Corundum is Transparent to translucent, Sapphire is transparent.
Which is harder, Corundum or Sapphire?
They are about equally hard, both near Mohs 9.
Which is more valuable, Corundum or Sapphire?
Sapphire is usually the more valuable of the two: a typical collector specimen runs about $5000 against $20 for Corundum, and premium Sapphire can reach $50000 or more.
