Actinolite

{{Short description|Mineral}} {{about|the mineral|the community in Canada|Actinolite, Ontario}} {{redirect|Uralite|the rail stop|Uralite Halt railway station}} {{Infobox mineral |boxbgcolor=#987630| name = Actinolite | boxtextcolor = #fff | category = Inosilicates | image = Actinolite Portugal.jpg | imagesize = 260px | alt = | caption = Actinolite crystal from Portugal | formula = Ca₂(Mg_4.5-2.5Fe²⁺_0.5-2.5) <br/>Si₈O₂₂(OH)₂ |IMAsymbol=Act<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 9.DE.10 | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''C2/m'' | color = pale to dark green, yellowish green, blue and black. White or grey when in asbestos | habit = bladed, fibrous, radial | twinning = simple or lamellar | cleavage = perfect along {110}. | fracture = uneven | mohs = 5–6 | luster = vitreous to dull | polish = vitreous | refractive = n_α = 1.613–1.628<br/> n_β = 1.627–1.644<br/> n_γ = 1.638–1.655 | opticalprop = Biaxial (−) | 2V = 78–82° (calc), 84–73° (meas) | dispersion = r < v | birefringence = 0.0250–0.0270 | pleochroism = moderate, yellow to dark green (in stones that are transparent) | fluorescence= inert | absorption = faint line at 503 nm | streak = white | gravity = 3.00 (+0.10, -0.05) | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = translucent to transparent | other = |references = <ref>[http://www.mindat.org/min-18.html Actinolite]. Mindat.org</ref><ref name=wembmin>[https://www.webmineral.com/data/Actinolite.shtml Actinolite]. Webmineral.org</ref><ref>[http://rruff.geo.arizona.edu/doclib/hom/actinolite.pdf Actinolite]. Handbook of mineralogy</ref><ref name="GRG">Gem Reference Guide. City: Gemological Institute of America (GIA), 1988. {{ISBN|0-87311-019-6}}</ref><ref>[http://pubsites.uws.edu.au/ima-cnmnc/ IMA Master List]</ref> }}

[[File:Actinolite-47621.jpg|thumb|upright=0.3|Gem-quality actinolite blade, from Mogok, Burma]]

'''Actinolite''' is an amphibole silicate mineral with the chemical formula {{nowrap|Ca₂(Mg_4.5–2.5Fe²⁺_0.5–2.5)Si₈O₂₂(OH)₂}}.

==Etymology== The name ''actinolite'' is derived from the Greek word ''aktis'' ({{lang|grc|ἀκτίς}}), meaning "beam" or "ray", because of the mineral's fibrous nature.<ref name=wembmin/>

==Mineralogy== Actinolite is an intermediate member in a solid-solution series between magnesium-rich tremolite, {{nowrap|Ca₂(Mg_5.0-4.5Fe²⁺_0.0-0.5)Si₈O₂₂(OH)₂}}, and iron-rich ferro-actinolite, {{nowrap|☐Ca₂(Mg_2.5-0.0Fe²⁺_2.5-5.0)Si₈O₂₂(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.

Fibrous actinolite is one of the six recognised types of asbestos, the fibres being so small that they can enter the lungs and damage the alveoli. Actinolite asbestos was once mined along Jones Creek at Gundagai, Australia.

==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).<ref name="GRG"/>

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.<ref name="GRG"/>

==See also== {{Portal|Earth sciences}} * Classification of minerals * List of minerals

==References== {{Reflist}} * Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York {{ISBN|0-471-80580-7}} {{Wiktionary}} {{Commons category}}

Category:Inosilicates Category:Calcium minerals Category:Magnesium minerals Category:Iron(II) minerals Category:Asbestos Category:Amphibole group Category:Monoclinic minerals Category:Minerals in space group 12 Category:Gemstones