Comparison · Minerals vs Silicate Minerals
Kyanite vs Sillimanite
Kyanite and Sillimanite are easy to confuse. Sillimanite is harder (Mohs 7) than Kyanite (Mohs 5), so Sillimanite 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 Kyanite and Sillimanite
- Sillimanite is harder (Mohs 7) than Kyanite (Mohs 5), so Sillimanite will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
- Hold a thin edge to the light: Kyanite is translucent, Sillimanite is transparent.
- They overlap in green, but Kyanite also comes in blue, orange, and black and Sillimanite also comes in white, gray, brown, and yellow.
- Well-formed crystals give it away: Kyanite is triclinic, Sillimanite is orthorhombic.
Kyanite vs Sillimanite properties
| Property | Kyanite | Sillimanite |
|---|---|---|
| Type | Minerals | Silicate Minerals |
| Mohs hardness | 5 | 7 |
| Luster | vitreous | vitreous |
| Streak | White | White |
| Transparency | translucent | transparent |
| Specific gravity | 3.6 | 3.24 |
| Crystal system | triclinic | orthorhombic |
| Common colors | Blue, Green, Orange, Black | White, Gray, Brown, Pale green, Yellow |
| Rarity | uncommon | uncommon |
| Typical specimen value | $10–$300+ | $10–$450+ |
Which is more valuable?
Sillimanite is usually the more valuable of the two: a typical collector specimen runs about $70 against $50 for Kyanite, and premium Sillimanite can reach $450 or more.
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).
About Sillimanite
Sillimanite is an aluminum silicate mineral that forms slender prismatic crystals or fibrous masses, the fibrous variety being called fibrolite. It is one of three aluminosilicate minerals that share the same composition but differ in structure.
Kyanite vs Sillimanite FAQ
Is Kyanite the same as Sillimanite?
No. Kyanite is a mineral while Sillimanite is a silicate mineral. Sillimanite is harder (Mohs 7) than Kyanite (Mohs 5), so Sillimanite 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 Kyanite from Sillimanite?
Sillimanite is harder (Mohs 7) than Kyanite (Mohs 5), so Sillimanite will scratch Kyanite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Hold a thin edge to the light: Kyanite is translucent, Sillimanite is transparent. They overlap in green, but Kyanite also comes in blue, orange, and black and Sillimanite also comes in white, gray, brown, and yellow.
Which is harder, Kyanite or Sillimanite?
Sillimanite is harder: Mohs 7 against Mohs 5 for Kyanite.
Which is more valuable, Kyanite or Sillimanite?
Sillimanite is usually the more valuable of the two: a typical collector specimen runs about $70 against $50 for Kyanite, and premium Sillimanite can reach $450 or more.
