RocksdayAtacamite vs Dioptase
How to tell them apart
A copper chloride forming dark emerald-green crystals in very dry climates.
Photo: Ivar Leidus, CC BY-SA 4.0
An intensely emerald-green copper silicate that forms glittering short crystals.
Photo: Géry PARENT, CC BY-SA 4.0
Quick tests
- Hardness: Dioptase is clearly harder: Mohs 5 versus 3–3.5.
- Streak (rub on unglazed porcelain): Atacamite leaves a apple green streak; Dioptase leaves green.
Key differences
- Dioptase is brighter green and harder.
Side by side
| Property | Atacamite | Dioptase |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3–3.5 | 5 |
| Luster | Adamantine to vitreous | Vitreous |
| Streak | Apple green | Green |
| Colors | Green | Green |
| Crystal system | Orthorhombic | Trigonal |
| Specific gravity | 3.75–3.77 | 3.28–3.35 |
| Formula | Cu₂Cl(OH)₃ | CuSiO₂(OH)₂ |
| Found in | Atacama Desert, Chile; Burra, South Australia | Tsumeb, Namibia; Altyn-Tyube, Kazakhstan |
Properties that are the same for both are grayed out.
How to identify atacamite
- Deep emerald to blackish green slender prisms.
- Apple-green streak.
- Doesn't fizz in acid.
Crystal system: Orthorhombic
Full Atacamite guide →How to identify dioptase
- Vivid emerald green, often a sparkling crystal crust.
- Short six-sided crystals with rhombic tips.
- Hardness 5 — a knife scratches it.
Crystal system: Trigonal
Full Dioptase guide →More comparisons
Could you tell them apart from a blurry close-up?
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