RocksdayAegirine vs Black Tourmaline
The quickest way to tell Aegirine from Black Tourmaline: Aegirine leaves a yellowish gray streak; Black Tourmaline leaves white.
A sodium-iron pyroxene that forms black to greenish-black prisms in rocks that are poor in silica.
Photo: Ivar Leidus, CC BY-SA 4.0
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
Quick tests
- Streak (rub on unglazed porcelain): Aegirine leaves a yellowish gray streak; Black Tourmaline leaves white.
Key differences
- Schorl has no cleavage and a triangular cross-section.
Side by side
| Property | Aegirine | Black Tourmaline |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6 | 7–7.5 |
| Luster | Vitreous | Vitreous |
| Streak | Yellowish gray | White |
| Colors | Black, Green, Brown | Black |
| Crystal system | Monoclinic | Trigonal |
| Specific gravity | 3.5–3.6 | 3.1–3.25 |
| Formula | NaFeSi₂O₆ | NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄ |
| Found in | Mount Malosa, Malawi; Mont Saint-Hilaire, Quebec | Erongo, Namibia; Minas Gerais, Brazil |
Properties that are the same for both are grayed out.
How to identify aegirine
- Black or dark green slender prisms.
- Two cleavages crossing at nearly 90°.
- Hardness about 6. Pale yellowish streak.
Crystal system: Monoclinic
Full Aegirine guide →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 →More comparisons
Frequently asked questions
What is the difference between aegirine and black tourmaline?
Aegirine is a mineral (NaFeSi₂O₆) with a Mohs hardness of 6 and a vitreous luster, usually black, green or brown. Black Tourmaline is a mineral with a Mohs hardness of 7–7.5 and a vitreous luster, usually black.
How can you tell aegirine from black tourmaline?
Aegirine leaves a yellowish gray streak; Black Tourmaline leaves white. Schorl has no cleavage and a triangular cross-section.
Could you tell them apart from a blurry close-up?
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