Actinolite (Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂) is the iron-bearing intermediate member of the tremolite-ferro-actinolite calcic amphibole series. Its name from Greek “aktinos” (ray) refers to its radiating fibrous habit. Actinolite forms in greenschist-facies metamorphic rocks and serpentinized ultramafic bodies. Compact green Actinolite aggregates produce nephrite jade alongside Tremolite.
Key Facts
- Mohs hardness 5–6.
- Monoclinic amphibole; intermediate Fe content between Tremolite and ferro-actinolite.
- Diagnostic green color from Fe²⁺ substitution for Mg.
- “Cat’s eye” Actinolite (chatoyant fibrous variety) is gem-cut.
- Common in greenschist-facies metamorphic rocks worldwide.
Notable Localities
Greiner Alm (Austria) is the type-locality. Madagascar, Brazil, and Taiwan yield gem-quality material. Actinolite-tremolite continuum forms nephrite at Hetian.
Found at these Localities
- Hetian (Khotan) Jade District (和田玉矿区)
- Eastern Brazilian Pegmatite Province (巴西东部伟晶岩省)
