Image: Andrew Silver (Public domain)
monocliniccommonSilicates (Inosilicate, Amphibole Group)
Actinolite
Ca2(Mg,Fe2+)5Si8O22(OH)2
This specimen displays dark green to blackish-green, elongated, prismatic crystals of actinolite, forming a dense, somewhat fibrous aggregate. The overall appearance is opaque with a vitreous to silky luster.
Actinolite Physical Properties
Mohs Hardness
5.5Crystal System
monoclinicLuster
vitreousStreak Color
whiteCleavage
perfect on {110} at 56° and 124°Fracture
unevenSpecific Gravity
3.05Colors
green, dark green, grayish-green, blackish-greenTransparency
translucentType Locality
Worldwide, common in metamorphic terrains (e.g., Alps, USA, Canada)Mineral Group
Silicates (Inosilicate, Amphibole Group)Uses
collector, component of nephrite jade, rock-forming mineralAssociated Minerals
quartz, epidote, chlorite, talc, serpentine, garnetRarity
commonGeological Context
Actinolite is a characteristic mineral of low-to-medium grade regional metamorphism, particularly in greenschist facies, where it forms from the alteration of mafic minerals in igneous rocks. It can also be found in contact metamorphic zones and altered ultramafic rocks.
