Actinolite
Image: Andrew Silver (Public domain)
Mineral NameActinolite
Chemical FormulaCa2(Mg,Fe2+)5Si8O22(OH)2
Mohs Hardness5.5
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite
Cleavageperfect on {110} at 56° and 124°
Fractureuneven
Specific Gravity3.05
Colorsgreen, dark green, grayish-green, blackish-green
Transparencytranslucent
Type LocalityWorldwide, common in metamorphic terrains (e.g., Alps, USA, Canada)
Mineral GroupSilicates (Inosilicate, Amphibole Group)
Usescollector, component of nephrite jade, rock-forming mineral
Associated Mineralsquartz, epidote, chlorite, talc, serpentine, garnet
Raritycommon
Description
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.
Geological 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.
