Image: Andrew Silver (Public domain)
monocliniccommonSilicates (Inosilicates, Amphibole Group)
Actinolite
Ca2(Mg,Fe2+)5Si8O22(OH)2
This specimen displays dark green to greenish-black, fibrous to prismatic actinolite crystals, forming an aggregate. A pen is included for scale, highlighting the size of the mineral formation.
Actinolite Physical Properties
Mohs Hardness
5.5Crystal System
monoclinicLuster
vitreousStreak Color
whiteCleavage
Perfect on {110} at 56° and 124° (amphibole cleavage)Fracture
unevenSpecific Gravity
3Colors
green, dark green, greenish-blackTransparency
translucentType Locality
Worldwide in metamorphic terrains, e.g., Alps, California, NorwayMineral Group
Silicates (Inosilicates, Amphibole Group)Uses
collector's specimens, component of nephrite jade, indicator mineral in metamorphic rocksAssociated Minerals
talc, chlorite, epidote, garnet, quartz, albiteRarity
commonGeological Context
Actinolite is a common metamorphic mineral, typically forming in greenschist facies metamorphic rocks from the alteration of mafic igneous rocks or magnesium-rich sedimentary rocks. It is also found in contact metamorphic aureoles.
