RocksdayPrehnite vs Smithsonite
How to tell them apart
A pale green silicate that forms bubbly, translucent crusts, often with black epidote needles.
Photo: Ivar Leidus, CC BY-SA 4.0
Zinc carbonate forming lustrous, bubbly crusts in pastel blue, green, pink and yellow.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Scratch glass: Prehnite scratches glass (Mohs 6–6.5); Smithsonite can't (Mohs 4.5).
- Acid (vinegar or dilute HCl): Smithsonite fizzes weakly, or only when powdered or warmed; Prehnite doesn't.
- Heft: Smithsonite feels noticeably heavier for its size (specific gravity 4.4–4.5 vs 2.8–2.95).
Key differences
- Smithsonite is heavier and fizzes in acid.
- Prehnite is harder and lighter.
Side by side
| Property | Prehnite | Smithsonite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6–6.5 | 4.5 |
| Luster | Vitreous to pearly | Vitreous to pearly |
| Streak | White | White |
| Colors | Green, Yellow, White | Blue, Green, Pink, Yellow |
| Crystal system | Orthorhombic | Trigonal |
| Specific gravity | 2.8–2.95 | 4.4–4.5 |
| Formula | Ca₂Al(AlSi₃O₁₀)(OH)₂ | ZnCO₃ |
| Found in | Wave Hill, Australia; Kayes, Mali | Kelly mine, New Mexico; Tsumeb, Namibia |
Properties that are the same for both are grayed out.
How to identify prehnite
- Pale apple-green to yellowish, translucent.
- Bubbly, rounded crusts or bow-tie aggregates.
- Hardness about 6.
Crystal system: Orthorhombic
Full Prehnite guide →How to identify smithsonite
- Botryoidal crusts with a satiny, pearly sheen.
- Heavy for its look.
- Fizzes in warm acid.
Crystal system: Trigonal
Full Smithsonite guide →More comparisons
Could you tell them apart from a blurry close-up?
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