Actinolite

Physical Properties
Chemical formula Ca2(Fe,Mg)5Si8O22(OH)2
Class Inosilicate
Double chains of linked tetrahedra
Crystal system Monoclinic
Habit Acicular, typically radiating
or forming parallel aggregates
Columnar masses
Color Dark green
Hardness 5 to 6
Specific gravity 3.0 to 3.3
Cleavage Two perfect prismatic {110}
Fracture Uneven
Luster Vitreous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Colorless to green
Pleochroic
“60/120” cleavage (actually 56° and 124°)
XPL Upper 1st to 2nd order interference colors
δ 0.03
after Perkins, 332

Actinolite in Hand Sample

Hand sample

Actinolite in quartz

Actinolite replacing spinifex olivine in a meta-komatiite

Scanning electron micrograph of actinolite

Actinolite in Thin Section

Thin Section GigaPans

Actinolite in actinolite schist, plane polars

Actinolite in actinolite schist, crossed polars

Actinolite, PPL

Actinolite, XPL

Further Reading

Actinolite at webmineral.com

Actinolite at mindat.org