Editorial Feature

Actinolite– Occurrence, Properties, and Distribution

Jun 13 2014

Actinolite was named by Richard Kirwan in 1794 after the Greek word for ray, based on the allusion to the mineral's common radiating fibrous habit.

Properties of Actinolite

The following are the key properties of actinolite:

Cell Data
- Space group: C2/m
- a = 9.891(1)
- b = 18.200 (1)
- c = 5.305(1)
- β = 104.64(1)°
- Z = 2

Crystal Data
- Monoclinic
- Point group: 2/m
- As bladed crystals, to 15cm
- Columnar
- radiating fibrous to asbestiform
- granular to massive
- Twinning: Simple or lamellar, common || {1001}; lamellar, less common || {001}
- X-ray powder pattern: 2.719 (100), 2.543 (100), 3.401 (80), 8.47 (70), 4.91 (70), 3.143 (70), 2.959 (70)

Chemical Composition

Elements	Content 1
SiO₂	55.17
MgO	16.21
CaO	12.08
FeO	11.07
Al₂O₃	2.69
Na₂O	0.82
MnO	0.18
TiO₂	0.17
Total	98.39

Optical Properties
- Optical class: Biaxial (-)
- Pleochroism: Weak
- X = pale yellow, yellowish-green
- Y = pale yellow-green, green
- Z = pale green, deep greenish-blue
- Orientation: Y = b; Z^c = 14° - 18.5°
- Dispersion: r < v , weak; α = 1.613-1.646; β = 1.624-1.656; γ = 1.636-1.666
- 2V(meas.) = 79°-86°

Estimated Properties

Electron density	Bulk density (electron density) = 3.02 g/cm³ note: Specific gravity of actinolite = 3.04 g/cm³
Photoelectric	PE_Actinolite = 4.88 barns/electron U = PE_Actinolite x ρelectron density = 14.73 barns/cm³
Fermion index	Fermion index = 0.02 Boson index = 0.98
Radioactivity	Actinolite is not radioactive

How to Identify Actinolite

Actinolite can be identified in the field by its color variations, such as green, green-black, gray-green, and black. It has {110} perfect cleavage. This mineral has a vitreous luster, with white streak. The fracture on this mineral is splintery, thin, elongated fractures - caused due to the intersecting good cleavages.

The density of actinolite is 2.98 to 3.1 g/cm³, with a hardness of 5.5 – approximate to a knife blade.

Global Distribution

Actinolite is distributed in the following places:

Norway - From Zermatt, Valais, Switzerland. At Snarum and Arendal
USA - Gouverneur, St. Lawrence Co. New York; Franklin and Newton, Sussex Co. New Jersey; Chester, Windsor Co. Vermont; in the Fairfax quarry, Centreville, Fairfax Co. Virginia; Crestmore, Riverside Co. California; at Salida, Charee Co. Colorado. “Nephrite jade" occurs in the south and east of Lander, Fremont Co. Wyoming; north from Cape San Martin, Monterey Co. California; and around Jade Mountain, near the Kobuk River, Alaska
Canada - Along the Fraser River, British Columbia
New Zealand - Around Mt. Cook, South Island
China - Kunlun Mountains, Sinkiang Uighur Autonomous Region
Austria - On Mt. Greiner, Zillertal, and at Untersulzbachtal
Russia - From the Ural Mountains

Occurrence of Actinolite and Useful Mineral Association

Actinolite is produced by low-grade regional or contact metamorphism of magnesium carbonate, mafic, or ultramafic rocks; also in glaucophane-bearing blueschists.

It is often associated with minerals such as talc, chlorite, glaucophane, epidote, lawsonite, albite, and pumpellyite.