- a variety of amphibole, occurring in greenish bladed crystals or in masses.
- a green mineral of the amphibole group consisting of calcium magnesium iron silicate. Formula: Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2
- A greenish variety of amphibole. Actinolite is a monoclinic mineral, and occurs in long, slender, green needlelike crystals, or in fibrous, radiated forms in metamorphic rocks. Chemical formula: Ca2(Mg,Fe)5Si8O22OH2.