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Actinolite

Discovered in 1794;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca₂(Mg,Fe+)₅Si₈O₂₂(OH)₂

Calcium Magnesium Iron Silicate Hydroxide

Molecular Weight:

853.16 gm

Composition:

Sodium

0.59 %

Na

0.80 %

Na₂O

Calcium

8.60 %

Ca

12.03 %

CaO

Magnesium

9.71 %

Mg

16.11 %

MgO

Titanium

0.11 %

Ti

0.19 %

TiO₂

Manganese

0.13 %

Mn

0.17 %

MnO

Aluminum

1.39 %

Al

2.63 %

Al₂O₃

Iron

8.58 %

Fe

10.61 %

FeO / 0.47 % Fe₂O₃

Silicon

25.64 %

Si

54.86 %

SiO₂

Hydrogen

0.24 %

H

2.11 %

H₂O

Oxygen

45.01 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.10-20

Nickel-Strunz 10th Ed. ID:

9.DE.10

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Amphibole Group. Calcic Clino-Amphibole Subgroup. Actinolite-Tremolite Series. Actinolite-Ferro-Actinolite Series. Actinolite-Hornblende Series.

Members of Group:

Amphibole Group: Calcic Clino-Amphibole Subgroup, Mg-Fe-Mn-Li Ortho-Amphibole Subgroup, Mg-Mn-Fe-Li Clino-Amphibole Subgroup, Sodic Clino-Amphibole Subgroup

Members of Sub-Group:

Calcic Clino-Amphibole Subgroup: Actinolite, Barroisite, Cannilloite, Edenite, Ferro-Actinolite, Ferro-Aluminotschermakite, Ferro-Edenite, Ferro-Ferritschermakite, Ferrobarroisite, Ferrohornblende, Ferrokaersutite, Ferropargasite, Ferrorichterite, Ferro-Tschermakite, Ferrowinchite, Fluor-Cannilloite, Fluoro-Edenite, Fluoro-potassicrichterite, Hastingsite, IMA2009-091, Kaersutite, Katophorite, Magnesiohastingsite, Magnesiohornblende, Magnesiokatophorite, Magnesiosadanagaite, Magnesiotaramite, Pargasite, Parvo-Manganotremolite, Potassic-Ferrisadanagaite, Potassicpargasite, Potassicsadanagaite, Richterite, Taramite, Tremolite, Tschermakite, Winchite

Varieties:

Byssolite, Hotan Jade, Nephrite, Smaragdite

Synonyms:

Actinolithe, Actynolite, Attinoto, Stibolite, Stralite, Zillerthite, Zillertite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

As bladed crystals, to 15 cm; columnar, may be kinked or bent; radiating fibrous to asbestiform; granular to massive.

Twinning:

Simple or lamellar

Physical Properties

Cleavage:

[110] Distinct/Good

Fracture:

Splintery to Granular

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

3.03 - 3.24 (g/cm³)

Luminescence:

Non-fluorescent

Radioactivity:

Not Radioactive

Optical Properties

Color:

Bright green to grayish green; rarely orange to orangish brown.

Transparency:

Transparent to Translucent

Luster:

Vitreous (sometimes dull)

Refractive Index:

n_α= 1.613-1.646, n_β= 1.624-1.656, n_γ= 1.636-1.666  Biaxial ( - )

Birefringence:

0.023

Dispersion:

Weak

Pleochroism:

Weak

Occurances

Geological Setting:

Produced by low-grade regional or contact metamorphism of magnesium carbonate, mafic, or ultramamafic rocks; also in glaucophane-bearing blueschists.

Common Associations:

Talc, Epidote, Chlorite, Glaucophane, Pumpellyite, Lawsonite, Albite

Common Impurities:

Mn, Al, Na, K, Ti

Type Locality:

N

Year Discovered:

1794

View mineral photos:

Actinolite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Actinolite is a member of the Calcic Clino-Amphibole Subgroup of the Amphibole Group of minerals that includes Actinolite, Ferro-edenite, Kaersutite, Pargasite, Richterite and Tremolite. The Amphibole Group is an extensive and complex group of minerals currently divided into several sub-groups. Actinolite and Tremolite have almost the same chemical formula but differ in the amounts of iron and magnesium. Iron is relatively abscent in Tremolite. Actinolite is rarely facetable and faceted gems are usually very small since crystals are typically very fibrous. A large (over 1 carat), clean, faceted Actinolite gem is very rare. Actinolite ranges in color from pale to very dark green, even black and rarely dark orangish brown. It occurs as green needle inclusions in quartz much more often than a gem by itself.

Actinolite is named from the Greek words aktina meaning ray, due to its radiating fibrous habit, and lithos meaning stone.

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

Actinolite gems for sale: