Comparison · Minerals
Diopside vs Kyanite
Diopside and Kyanite are easy to confuse because both are minerals. Diopside is harder (Mohs 5.5–6.5) than Kyanite (Mohs 5), so Diopside 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 Diopside and Kyanite
- Diopside is harder (Mohs 5.5–6.5) than Kyanite (Mohs 5), so Diopside 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: Diopside is Transparent to translucent, Kyanite is translucent.
- They overlap in green, blue, and black, but Diopside also comes in white, gray, purple, and multicolored and Kyanite also comes in orange.
- Well-formed crystals give it away: Diopside is Monoclinic, Kyanite is triclinic.
Diopside vs Kyanite properties
| Property | Diopside | Kyanite |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 5.5–6.5 | 5 |
| Luster | Vitreous | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | translucent |
| Specific gravity | 3.2–3.3 | 3.6 |
| Crystal system | Monoclinic | triclinic |
| Common colors | Light to dark green, White, Gray, Blue-violet (violane), Black (chromian varieties) | 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 Diopside, and premium Kyanite can reach $300 or more.
About Diopside
Diopside is a calcium magnesium silicate pyroxene mineral, CaMgSi2O6, common in metamorphosed limestones and mafic to ultramafic igneous rocks. It typically forms stubby prismatic crystals with a nearly square cross-section, a hallmark of the pyroxene group's characteristic cleavage angles. Diopside's color ranges from colorless to deep green depending on iron and chromium content, and chromium-rich varieties are prized as gem material.
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).
Diopside vs Kyanite FAQ
Is Diopside the same as Kyanite?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Diopside is harder (Mohs 5.5–6.5) than Kyanite (Mohs 5), so Diopside 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 Diopside from Kyanite?
Diopside is harder (Mohs 5.5–6.5) than Kyanite (Mohs 5), so Diopside 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: Diopside is Transparent to translucent, Kyanite is translucent. They overlap in green, blue, and black, but Diopside also comes in white, gray, purple, and multicolored and Kyanite also comes in orange.
Which is harder, Diopside or Kyanite?
Diopside is harder: Mohs 5.5–6.5 against Mohs 5 for Kyanite.
Which is more valuable, Diopside or Kyanite?
Kyanite is usually the more valuable of the two: a typical collector specimen runs about $50 against $20 for Diopside, and premium Kyanite can reach $300 or more.
