Mineral Information and Data:

Actinolite
Ca2(Mg,Fe2+)5Si8O22(OH)2 [CNMNC approved formula]

Named from the Greek ακτίνα ("aktina") for "ray" and λίθος ("lithos") for "stone" in allusion to its fibrous nature.

IMA status : Valid species (Pre-IMA 1794) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
66.01.03a.02  
  (66) Inosilicate Double-Width Unbranched Chains, W=2
  (66.01) with P=2 amphibole configuration
  (66.01.03a) Group 2, the calcic amphiboles
  
Nickel-Strunz
(10th edition) :
09.DE.10
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C 2/m
Unit cell: a = 9.88 Å, b = 18.15 Å, c = 5.29 Å, b = 104.7°
Crystal Habit: Crystals long bladed; usually in fibrous to thin columnar aggregates, often radiated; massive
Twinning: Common parallel {100}, simple or lamellar; also parallel {001}, lamellar
  
Color: Light green to blackish green
Diaphaneity: Transparent to translucent
Luster: Vitreous or dull
Hardness (Mohs): 5 to 6
Measured Density: 3 to 3.44 g/cm3
Cleavage: 2; (110) good, (100) parting
Tenacity: Brittle,tough in fibrous aggregates ("nephrite jade")
Streak: White
  
Polymorphism and Series: Intermediate member of the series tremolite - ferro-actinolite
Geologic Setting: Produced by low-grade regional or contact metamorphism of magnesium
carbonate, mafic, or ultramafic rocks; also in glaucophane-bearing blueschists.
Mineral Association: Talc, epidote, chlorite, glaucophane, pumpellyite, lawsonite, albite
  
Synonyms/varieties: Jade (compact gem var.), nephrite (compact var.), byssolite (fibrous var.), smaragdite/uralite (replacing pyroxene), strahlstein, zillerite, zillerthite.
Other Properties: Gemstone Readily Available.

 

Actinolite
Actinolite with minor Phlogopite
Origin: Medicine Mountain, Custer Co., South Dakota, USA
Sample size: 10 x 5 x 5 cm
Photo : Tom Loomis

 

Actinolite
(zoom in of above)

 

Actinolite
Origin: Tiburon Peninsula, Marin Co., California, U.S.A.
Sample size: 3.5 x 5 cm
Photo : Diederik Visser

 

Actinolite
Green Actinolite crystals up to 3 cm in Talc matrix
Origin: Felbertal, Pinzgau, Austria
Sample size: 3.3 x 5 cm
Photo : Diederik Visser

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