Comparison · Minerals
Corundum vs Kyanite
Corundum and Kyanite are easy to confuse because both are minerals. Corundum is harder (Mohs 9) than Kyanite (Mohs 5), so Corundum will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Corundum and Kyanite
- Corundum is harder (Mohs 9) than Kyanite (Mohs 5), so Corundum will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
- Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Kyanite leaves white.
- Hold a thin edge to the light: Corundum is Transparent to translucent, Kyanite is translucent.
- They overlap in blue and green, but Corundum also comes in red, clear, yellow, pink, and gray and Kyanite also comes in orange and black.
- Well-formed crystals give it away: Corundum is Trigonal, Kyanite is triclinic.
Corundum vs Kyanite properties
| Property | Corundum | Kyanite |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 9 | 5 |
| Luster | Adamantine to vitreous | vitreous |
| Streak | White (colorless) | White |
| Transparency | Transparent to translucent | translucent |
| Specific gravity | 3.95–4.10 | 3.6 |
| Crystal system | Trigonal | triclinic |
| Common colors | Red (ruby), Blue (sapphire), Colorless, Yellow, Green, Pink, Gray | Blue, Green, Orange, Black |
| Rarity | common | uncommon |
| Typical specimen value | $2–$150+ | $10–$300+ |
Which is more valuable?
Kyanite is usually the more valuable of the two: a typical collector specimen runs about $50 against $20 for Corundum, and premium Kyanite can reach $300 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 Kyanite
Kyanite is a blue silicate mineral unique for having different hardness values depending on the direction of scratch (4-5 lengthwise, 6-7 crosswise).
Corundum vs Kyanite FAQ
Is Corundum the same as Kyanite?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Corundum is harder (Mohs 9) than Kyanite (Mohs 5), so Corundum will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
How can you tell Corundum from Kyanite?
Corundum is harder (Mohs 9) than Kyanite (Mohs 5), so Corundum will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Kyanite leaves white. Hold a thin edge to the light: Corundum is Transparent to translucent, Kyanite is translucent.
Which is harder, Corundum or Kyanite?
Corundum is harder: Mohs 9 against Mohs 5 for Kyanite.
Which is more valuable, Corundum or Kyanite?
Kyanite is usually the more valuable of the two: a typical collector specimen runs about $50 against $20 for Corundum, and premium Kyanite can reach $300 or more.
