RocksdayPeridotite vs Serpentinite
How to tell them apart
A dense green rock of olivine and pyroxene — the main rock of Earth's upper mantle.
Photo: Shannon Heinle, CC0
Rock of serpentine minerals, formed when mantle rock reacts with seawater. Slick, green and mottled.
Photo: Gabriel HM, CC BY-SA 4.0
Quick tests
- Scratch glass: Peridotite scratches glass (Mohs 6–7); Serpentinite can't (Mohs 3–5).
Key differences
- Serpentinite is altered peridotite: waxy and slick.
Side by side
| Property | Peridotite | Serpentinite |
|---|---|---|
| Type | Igneous rock | Metamorphic rock |
| Mohs hardness | 6–7 | 3–5 |
| Luster | Granular | Waxy to greasy |
| Colors | Green, Black, Brown | Green, Black |
| Crystal system / structure | Coarse-grained (ultramafic) | Massive, often sheared |
| Specific gravity | 3.1–3.4 | 2.5–2.8 |
| Found in | Samail ophiolite, Oman; Tablelands, Newfoundland | California Coast Ranges; Newfoundland |
Properties that are the same for both are grayed out.
How to identify peridotite
- Green, coarse and very heavy.
- Mostly glassy olivine grains.
- Weathers to a rusty brown crust.
Structure: Coarse-grained (ultramafic)
Full Peridotite guide →How to identify serpentinite
- Green to black with a waxy, slippery look.
- Polished, scaly surfaces where it was sheared.
- Softer than it looks.
Structure: Massive, often sheared
Full Serpentinite guide →More comparisons
Could you tell them apart from a blurry close-up?
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