RocksdayAstrophyllite vs Black Tourmaline
The quickest way to tell Astrophyllite from Black Tourmaline: Black Tourmaline scratches glass (Mohs 7–7.5); Astrophyllite can't (Mohs 3).
A titanium silicate that grows as bronze, star-like sprays of flat blades.
Photo: Modris Baum, Public domain
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
- Scratch glass: Black Tourmaline scratches glass (Mohs 7–7.5); Astrophyllite can't (Mohs 3).
- Streak (rub on unglazed porcelain): Astrophyllite leaves a brown streak; Black Tourmaline leaves white.
Key differences
- Schorl forms hard prisms, not soft bronze stars.
Side by side
| Property | Astrophyllite | Black Tourmaline |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3 | 7–7.5 |
| Luster | Submetallic to pearly | Vitreous |
| Streak | Brown | White |
| Colors | Brown, Gold, Yellow | Black |
| Crystal system | Triclinic | Trigonal |
| Specific gravity | 3.2–3.4 | 3.1–3.25 |
| Formula | — | NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄ |
| Found in | Khibiny, Kola Peninsula, Russia; Pikes Peak area, Colorado | Erongo, Namibia; Minas Gerais, Brazil |
Properties that are the same for both are grayed out.
How to identify astrophyllite
- Golden-brown blades in starbursts.
- A copper coin scratches it.
- Blades are brittle, not elastic like mica.
Crystal system: Triclinic
Full Astrophyllite 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 astrophyllite and black tourmaline?
Astrophyllite is a mineral with a Mohs hardness of 3 and a submetallic to pearly luster, usually brown, golden or yellow. Black Tourmaline is a mineral with a Mohs hardness of 7–7.5 and a vitreous luster, usually black.
How can you tell astrophyllite from black tourmaline?
Black Tourmaline scratches glass (Mohs 7–7.5); Astrophyllite can't (Mohs 3). Astrophyllite leaves a brown streak; Black Tourmaline leaves white. Schorl forms hard prisms, not soft bronze stars.
Could you tell them apart from a blurry close-up?
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