RocksdayDiamond vs Quartz
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
The second most abundant mineral in Earth's crust. Clear crystals grow as six-sided prisms capped by a pointed termination, and quartz shows up as grains in sand, granite and countless other rocks.
Photo: Didier Descouens, CC BY-SA 4.0
Quick tests
- Hardness: Diamond is clearly harder: Mohs 10 versus 7.
- Streak (rub on unglazed porcelain): Diamond leaves a none (harder than a streak plate) streak; Quartz leaves white.
- Heft: Diamond feels noticeably heavier for its size (specific gravity 3.51–3.53 vs 2.65).
Key differences
- Quartz is far softer and has a glassy, not adamantine, luster.
Side by side
| Property | Diamond | Quartz |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 10 | 7 |
| Luster | Adamantine | Vitreous |
| Streak | None (harder than a streak plate) | White |
| Colors | Clear, Yellow, Brown, Gray | Clear, White, Gray |
| Crystal system | Cubic | Trigonal |
| Specific gravity | 3.51–3.53 | 2.65 |
| Formula | C | SiO₂ |
| Found in | Jwaneng, Botswana; Yakutia, Russia | Hot Springs, Arkansas; Minas Gerais, Brazil |
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 quartz
- Scratches glass easily and can't be scratched by a steel knife.
- Six-sided prisms with pointed ends when it forms crystals.
- Breaks with curved, shell-like (conchoidal) fractures — no flat cleavage planes.
- Does not fizz in vinegar or dilute acid.
Crystal system: Trigonal
Full Quartz guide →More comparisons
Could you tell them apart from a blurry close-up?
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