RocksdayDumortierite vs Lapis Lazuli
How to tell them apart
A denim-blue aluminum borosilicate, usually as fibrous masses or embedded in quartz.
Photo: Géry PARENT, CC BY-SA 3.0
A deep-blue rock made mostly of the mineral lazurite, flecked with golden pyrite and white calcite.
Photo: Hannes Grobe, CC BY-SA 2.5
Quick tests
- Hardness: Dumortierite is clearly harder: Mohs 7–8.5 versus 5–5.5.
- Acid (vinegar or dilute HCl): Lapis Lazuli fizzes weakly, or only when powdered or warmed; Dumortierite doesn't.
- Texture: Lapis Lazuli is a rock — a mix of grains or minerals; Dumortierite is a single mineral.
Key differences
- Lapis has gold pyrite flecks.
Side by side
| Property | Dumortierite | Lapis Lazuli |
|---|---|---|
| Type | Mineral | Metamorphic rock |
| Mohs hardness | 7–8.5 | 5–5.5 |
| Luster | Vitreous to dull | Dull to vitreous |
| Streak | White | — |
| Colors | Blue, Purple | Blue, Gold, White |
| Crystal system / structure | Orthorhombic | Granular, massive |
| Specific gravity | 3.3–3.4 | 2.7–2.9 |
| Formula | Al₇BO₃(SiO₄)₃O₃ | — |
| Found in | Madagascar; Brazil | Sar-e-Sang, Afghanistan; Coquimbo, Chile |
Properties that are the same for both are grayed out.
How to identify dumortierite
- Denim blue to violet, opaque and fibrous.
- Very hard and tough.
- Often speckled through quartz.
Crystal system: Orthorhombic
Full Dumortierite guide →How to identify lapis lazuli
- Intense ultramarine blue.
- Glittering gold pyrite flecks.
- White patches of calcite.
- Light blue streak.
Structure: Granular, massive
Full Lapis Lazuli guide →More comparisons
Could you tell them apart from a blurry close-up?
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