RocksdayBlack Tourmaline vs Obsidian
The quickest way to tell Black Tourmaline from Obsidian: Black Tourmaline is clearly harder: Mohs 7–7.5 versus 5–5.5.
Schorl, the iron tourmaline and the most common species of the group. Opaque black prisms with a triangular cross-section.
Photo: Parent Géry, CC BY-SA 3.0
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
Quick tests
- Hardness: Black Tourmaline is clearly harder: Mohs 7–7.5 versus 5–5.5.
- Texture: Obsidian is a rock — a mix of grains or minerals; Black Tourmaline is a single mineral.
Key differences
- Obsidian is glass: softer, lighter, and it breaks in smooth curves with no crystal faces.
- Schorl is harder, has crystal faces and a white streak. Obsidian breaks like glass.
Side by side
| Property | Black Tourmaline | Obsidian |
|---|---|---|
| Type | Mineral | Igneous rock |
| Mohs hardness | 7–7.5 | 5–5.5 |
| Luster | Vitreous | Glassy |
| Streak | White | — |
| Colors | Black | Black, Brown, Red |
| Crystal system / structure | Trigonal | Glassy |
| Specific gravity | 3.1–3.25 | 2.35–2.6 |
| Formula | NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄ | — |
| Found in | Erongo, Namibia; Minas Gerais, Brazil | Glass Buttes, Oregon; Yellowstone, Wyoming |
Properties that are the same for both are grayed out.
How to identify black tourmaline
- Black prisms with lengthwise grooves.
- A broken end is a rounded triangle, not a circle.
- Hard — scratches glass. White streak, not black.
- No cleavage. A magnet does not stick.
Crystal system: Trigonal
Full Black Tourmaline guide →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 →More comparisons
Frequently asked questions
What is the difference between black tourmaline and obsidian?
Black Tourmaline is a mineral with a Mohs hardness of 7–7.5 and a vitreous luster, usually black. Obsidian is an igneous rock with a Mohs hardness of about 5–5.5 and a glassy luster, usually black, brown or red.
How can you tell black tourmaline from obsidian?
Black Tourmaline is clearly harder: Mohs 7–7.5 versus 5–5.5. Obsidian is a rock — a mix of grains or minerals; Black Tourmaline is a single mineral. Obsidian is glass: softer, lighter, and it breaks in smooth curves with no crystal faces. Schorl is harder, has crystal faces and a white streak. Obsidian breaks like glass.
Could you tell them apart from a blurry close-up?
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