RocksdayDatolite vs Prehnite
How to tell them apart
A calcium borosilicate forming pale green glassy crystals, or porcelain-like nodules in Michigan's copper country.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A pale green silicate that forms bubbly, translucent crusts, often with black epidote needles.
Photo: Ivar Leidus, CC BY-SA 4.0
Key differences
- Prehnite forms bubbly crusts rather than sharp crystals.
Side by side
| Property | Datolite | Prehnite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5–5.5 | 6–6.5 |
| Luster | Vitreous | Vitreous to pearly |
| Streak | White | White |
| Colors | Green, White, Pink, Red | Green, Yellow, White |
| Crystal system | Monoclinic | Orthorhombic |
| Specific gravity | 2.9–3 | 2.8–2.95 |
| Formula | CaBSiO₄(OH) | Ca₂Al(AlSi₃O₁₀)(OH)₂ |
| Found in | Keweenaw Peninsula, Michigan; New Jersey | Wave Hill, Australia; Kayes, Mali |
Properties that are the same for both are grayed out.
How to identify datolite
- Pale green, many-faced glassy crystals.
- Michigan nodules look like porcelain, often tinted by copper.
- Hardness about 5.
Crystal system: Monoclinic
Full Datolite guide →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 →More comparisons
Could you tell them apart from a blurry close-up?
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