RocksdayDiamond vs Zircon
How to tell them apart
Pure carbon crystallized deep in the mantle and carried up in kimberlite eruptions. The hardest natural material.
Photo: DGPC/ADF Luísa Oliveira, CC0
A heavy, brilliant silicate found as small crystals in many rocks. Natural zircon is not the same as synthetic cubic zirconia.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Hardness: Diamond is clearly harder: Mohs 10 versus 7.5.
- Streak (rub on unglazed porcelain): Diamond leaves a none (harder than a streak plate) streak; Zircon leaves white.
- Heft: Zircon feels noticeably heavier for its size (specific gravity 4.6–4.7 vs 3.51–3.53).
Key differences
- Diamond is much harder and doesn't show doubled facet edges.
Side by side
| Property | Diamond | Zircon |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 10 | 7.5 |
| Luster | Adamantine | Adamantine |
| Streak | None (harder than a streak plate) | White |
| Colors | Clear, Yellow, Brown, Gray | Brown, Red, Yellow, Blue, Clear |
| Crystal system | Cubic | Tetragonal |
| Specific gravity | 3.51–3.53 | 4.6–4.7 |
| Formula | C | ZrSiO₄ |
| Found in | Jwaneng, Botswana; Yakutia, Russia | Sri Lanka; Ratanakiri, Cambodia |
Properties that are the same for both are grayed out.
How to identify diamond
- Scratches everything — including corundum.
- Greasy-looking, extremely bright luster even in rough crystals.
- Often octahedral with slightly curved faces.
- Water beads up on its surface.
Crystal system: Cubic
Full Diamond guide →How to identify zircon
- Square prisms capped with pyramids.
- Very bright luster and heavy for its size.
- Facet edges look doubled through a cut stone.
Crystal system: Tetragonal
Full Zircon guide →More comparisons
Could you tell them apart from a blurry close-up?
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