Quick Facts
Formation & Origin
Actinolite is a member of the amphibole mineral group that forms during metamorphism of mafic (magnesium and iron-rich) rocks at moderate temperatures and pressures. It's a key indicator mineral of the greenschist metamorphic facies, representing conditions of approximately 300-500°C.
The mineral forms a solid solution series with tremolite (the magnesium-rich end member). When actinolite grows as densely interlocking microscopic fibers, the result is nephrite jade, one of the toughest natural materials. In other habits, it forms elongated prismatic crystals, sometimes radiating sprays, and occasionally fibrous aggregates.
The name comes from the Greek 'aktinos' (ray) and 'lithos' (stone), referring to its common radiating crystal habit. Note: fibrous actinolite is a form of asbestos (actinolite asbestos) and should not be disturbed in its fibrous form. Crystal specimens are safe to handle normally.
Identification Guide
Actinolite is identified by its dark green color, elongated prismatic to bladed crystal habit, two cleavage directions at approximately 56 and 124 degrees (characteristic of amphiboles), and association with metamorphic rocks.
Distinguish from epidote (pistachio green, different cleavage angle), hornblende (darker, different composition), and chrome diopside (single good cleavage, pyroxene). The double cleavage at approximately 56/124 degrees is the most reliable amphibole identifier.
Spotting Fakes
Actinolite crystal specimens are not commonly faked. The main issues are: (1) confusion with other green amphiboles or pyroxenes, and (2) marketing fibrous actinolite as a metaphysical stone when it should be handled carefully. Nephrite jade (which is fibrous actinolite-tremolite) is frequently faked with serpentine or dyed quartzite, but this is addressed under the nephrite entry.
Cultural & Metaphysical Traditions
Presented as cultural traditions, not scientific evidence
Actinolite is considered a shield stone in crystal healing, associated with protecting the energy body and maintaining healthy boundaries. Its status as the raw material of nephrite jade connects it to jade's long tradition of wisdom and moral virtue. Practitioners use it for aligning actions with values and building resilience. NOTE: Avoid fibrous specimens for handling. Crystal specimens are safe.
Where It's Found
Classic locality for crystal specimens
Nephrite jade deposits (fibrous actinolite)
Nephrite jade from actinolite-tremolite
Crystal specimens and cat's eye material
Price Guide
Good to Know
Scratch test: At hardness 5.5, Actinolite resists scratching from a knife but can be scratched by quartz. Best for pendants and earrings rather than rings.
Sources: Found in 4 notable locations worldwide, from Austria to Madagascar.
Heft test: Actinolite has average mineral density (3.00-3.44). It feels about as heavy as you'd expect from a stone its size.
Related Minerals
Fibrous actinolite-tremolite, one of the two jades
Magnesium-rich end member of the series
Common dark amphibole, more complex chemistry