Actinolite crystal from Portugal
Category Mineral
Chemical formula Ca2(Mg,Fe)5Si8O22(OH)2
Color pale to dark green, yellowish green and black. White or grey when in asbestos form
Crystal habit bladed, fibrous, radial
Crystal system monoclinic – prismatic, H-M symbol (2/m), space group C2/m
Twinning simple or lamellar
Cleavage perfect along {110}.
Fracture uneven
Mohs scale hardness 5–6
Luster vitreous to dull
Streak white
Diaphaneity translucent to transparent
Specific gravity 3.00 (+0.10, -0.05)
Polish luster vitreous
Optical properties Biaxial (-)
Refractive index nα = 1.613–1.628
nβ = 1.627–1.644
nγ = 1.638–1.655
Birefringence 0.0250-0.0270
Pleochroism moderate, yellow to dark green (in stones that are transparent)
2V angle 78–82° (calc), 84-73° (meas)
Ultraviolet fluorescence inert
Absorption spectra faint line at 503 nm
References [1][2][3][4]

Actinolite is an amphibole silicate mineral with the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2.



The name actinolite is derived from the Greek word aktis (ἀκτίς), meaning "beam" or "ray", because of the mineral's fibrous nature.[2] (This word is also the origin of the name of the chemical element actinium.)


Actinolite is an intermediate member in a solid-solution series between magnesium-rich tremolite, Ca2Mg5Si8O22(OH)2, and iron-rich ferro-actinolite, Ca2Fe5Si8O22(OH)2. Mg and Fe ions can be freely exchanged in the crystal structure. Like tremolite, asbestiform actinolite is regulated as asbestos.


Actinolite is commonly found in metamorphic rocks, such as contact aureoles surrounding cooled intrusive igneous rocks. It also occurs as a product of metamorphism of magnesium-rich limestones.

The old mineral name uralite is at times applied to an alteration product of primary pyroxene by a mixture composed largely of actinolite. The metamorphosed gabbro or diabase rock bodies, referred to as epidiorite, contain a considerable amount of this uralitic alteration.

Some forms of asbestos are formed from fibrous actinolite, the fibres being so small that they can enter the lungs and damage the alveoli.


Some forms of actinolite are used as gemstones. One is nephrite, one of the two types of jade (the other being jadeite, a variety of pyroxene).[4]

Another gem variety is the chatoyant form known as cat's-eye actinolite. This stone is translucent to opaque, and green to yellowish green color. This variety has had the misnomer jade cat's-eye. Transparent actinolite is rare and is faceted for gem collectors. Major sources for these forms of actinolite are Taiwan and Canada. Other sources are Madagascar, Tanzania, and the United States.[4]

See also

DirkvdM rocks.jpg Earth sciences portal


  1. ^ Actinolite.
  2. ^ a b Actinolite.
  3. ^ Actinolite. Handbook of mineralogy
  4. ^ a b c Gem Reference Guide. City: Gemological Institute of America (GIA), 1988. ISBN 0-87311-019-6
  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7

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Look at other dictionaries:

  • Actinolite — Ac*tin o*lite, n. [Gr. ?, ?, ray + lite.] (Min.) A bright green variety of amphibole occurring usually in fibrous or columnar masses. [1913 Webster] …   The Collaborative International Dictionary of English

  • actinolite — [ak tin′ə līt΄] n. a dark colored, often greenish amphibole, Ca2 (Mg, Fe) 5 (Si8O22)(OH) 2, commonly found in schists and marbles …   English World dictionary

  • actinolite — actinolitic /ak tin l it ik, ak teuh nl /, adj. /ak tin l uyt , ak teuh nl /, n. Mineral. a variety of amphibole, occurring in greenish bladed crystals or in masses. [1825 35; ACTINO + LITE] * * * Colourless to green amphibole mineral, darkening… …   Universalium

  • actinolite — Amphibole Am phi*bole ([a^]m f[i^]*b[=o]l), n. [Gr. amfi bolos doubtful, equivocal, fr. amfiba llein to throw round, to doubt: cf. F. amphibole. Ha[ u]y so named the genus from the great variety of color and composition assumed by the mineral.]… …   The Collaborative International Dictionary of English

  • actinolite — aktinolitas statusas T sritis chemija apibrėžtis Mineralas. formulė Ca₂(Mg,Fe)₅[(OH,F)|Si₄O₁₁]₂ atitikmenys: angl. actinolite rus. актинолит …   Chemijos terminų aiškinamasis žodynas

  • actinolite — noun Date: 1796 a bright green or grayish green mineral of the amphibole group that is a silicate of calcium, magnesium, and iron occurring in fibrous, radiate, or columnar forms …   New Collegiate Dictionary

  • Actinolite — Actinote (minéral) Pour les articles homonymes, voir Actinote. Actinote Catégorie IX : silicates …   Wikipédia en Français

  • actinolite — noun A mineral with monoclinic crystals of the chemical formula Ca(Mg,Fe)SiO(OH), belonging to the amphibole group …   Wiktionary

  • actinolite — ac·ti·no·lì·te s.f. TS mineral. minerale del gruppo degli anfiboli monoclini, che si presenta in aggregati di cristalli fibrosi di colore variabile dal grigioverde al verde scuro {{line}} {{/line}} DATA: 1892. ETIMO: comp. di actino e 1 lite …   Dizionario italiano

  • actinolite — [ak tɪnəlʌɪt] noun a green mineral of the amphibole group occurring chiefly in metamorphic rocks and as a form of asbestos. Origin C18: from Gk aktis, aktin ray + lithos stone (because of the ray like crystals) …   English new terms dictionary

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