- Actinolite
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For the community in Canada, see Actinolite, Ontario.
Actinolite 
Actinolite crystal from PortugalGeneral Category Mineral Chemical formula Ca2(Mg,Fe)5Si8O22(OH)2 Identification 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 = 1.638–1.655Birefringence 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.
Contents
Etymology
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.)
Mineralogy
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.
Occurrence
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.
Gemology
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
References
- ^ Actinolite. Mindat.org
- ^ a b Actinolite. Webmineral.org
- ^ Actinolite. Handbook of mineralogy
- ^ 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
Categories:- Inosilicates
- Calcium minerals
- Magnesium minerals
- Iron minerals
- Asbestos
- Amphibole group
- Monoclinic minerals
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