RocksdayHornblende vs Tourmaline
How to tell them apart
A common black amphibole and the dark specks in many granites and diorites.
Photo: Shannon Heinle, CC0
A boron-bearing silicate found in more colors than almost any other gem. Black schorl is the most common form.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Hardness: Tourmaline is clearly harder: Mohs 7–7.5 versus 5–6.
- Streak (rub on unglazed porcelain): Hornblende leaves a gray-green streak; Tourmaline leaves white.
Key differences
- Tourmaline has no cleavage and a triangular cross-section.
Side by side
| Property | Hornblende | Tourmaline |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5–6 | 7–7.5 |
| Luster | Vitreous | Vitreous |
| Streak | Gray-green | White |
| Colors | Black, Green, Brown | Black, Green, Pink |
| Crystal system | Monoclinic | Trigonal |
| Specific gravity | 3–3.4 | 3–3.3 |
| Formula | Ca₂(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH)₂ | Complex borosilicate |
| Found in | Granites and diorites worldwide; Amphibolites | Mount Mica, Maine; San Diego County, California |
Properties that are the same for both are grayed out.
How to identify hornblende
- Black to dark green elongated prisms.
- Two cleavages meeting at about 56° and 124°.
- Shiny, splintery breaks.
Crystal system: Monoclinic
Full Hornblende guide →How to identify tourmaline
- Long prisms with lengthwise grooves (striations).
- Rounded-triangle cross-section when broken across.
- Hard — scratches glass.
- Gem crystals can change color from end to end ('watermelon').
Crystal system: Trigonal
Full Tourmaline guide →More comparisons
Could you tell them apart from a blurry close-up?
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