RocksdayActinolite vs Tremolite
How to tell them apart
A green amphibole forming radiating sprays of long crystals in greenschist rocks.
Photo: Didier Descouens, CC BY-SA 4.0
A white to gray amphibole formed when dolomitic marble is metamorphosed.
Photo: Didier Descouens, CC BY-SA 4.0
Key differences
- Tremolite is white to gray.
- Actinolite is green.
Side by side
| Property | Actinolite | Tremolite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5–6 | 5–6 |
| Luster | Vitreous to silky | Vitreous to silky |
| Streak | White | White |
| Colors | Green, Gray, Black | White, Gray, Purple |
| Crystal system | Monoclinic | Monoclinic |
| Specific gravity | 3–3.2 | 2.9–3.1 |
| Formula | Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂ | Ca₂Mg₅Si₈O₂₂(OH)₂ |
| Found in | Zillertal, Austria; Vermont | Gouverneur, New York; Switzerland |
Properties that are the same for both are grayed out.
How to identify actinolite
- Bright to dark green needles or blades.
- Often radiating like a star.
- Two amphibole cleavages.
Crystal system: Monoclinic
Full Actinolite guide →How to identify tremolite
- White to gray blades or fibers in marble.
- Amphibole cleavage angles of about 56° and 124°.
- Lavender variety (hexagonite) fluoresces.
Crystal system: Monoclinic
Full Tremolite guide →More comparisons
Could you tell them apart from a blurry close-up?
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