RocksdayObsidian vs Smoky Quartz
How to tell them apart
Natural volcanic glass, formed when silica-rich lava cools so fast that crystals have no time to grow.
Photo: Ji-Elle It feels nice and warm It feels like a love storm, CC BY-SA 3.0
Brown to nearly black quartz colored by natural radiation acting on traces of aluminum.
Photo: James St. John, CC BY 2.0
Quick tests
- Hardness: Smoky Quartz is clearly harder: Mohs 7 versus 5–5.5.
- Texture: Obsidian is a rock — a mix of grains or minerals; Smoky Quartz is a single mineral.
Key differences
- Obsidian is glass with no crystal faces, and softer.
Side by side
| Property | Obsidian | Smoky Quartz |
|---|---|---|
| Type | Igneous rock | Mineral |
| Mohs hardness | 5–5.5 | 7 |
| Luster | Glassy | Vitreous |
| Streak | — | White |
| Colors | Black, Brown, Red | Brown, Gray, Black |
| Crystal system / structure | Glassy | Trigonal |
| Specific gravity | 2.35–2.6 | 2.65 |
| Formula | — | SiO₂ |
| Found in | Glass Buttes, Oregon; Yellowstone, Wyoming | Swiss Alps; Cairngorm Mountains, Scotland |
Properties that are the same for both are grayed out.
How to identify obsidian
- Shiny, glass-like and usually black.
- Curved, shell-shaped (conchoidal) fractures with razor-sharp edges.
- Thin edges are translucent brown or gray.
- May show white 'snowflakes' or a gold/rainbow sheen.
Structure: Glassy
Full Obsidian guide →How to identify smoky quartz
- Transparent to translucent brown or gray quartz.
- Six-sided prisms with pointed ends.
- Hardness 7 and no cleavage.
Crystal system: Trigonal
Full Smoky Quartz guide →More comparisons
Could you tell them apart from a blurry close-up?
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