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Actinolite is an
amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Amphiboles can be gree ...
silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide) SiO2 is usually cons ...
with the chemical formula .


Etymology

The name ''actinolite'' is derived from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of ...
word ''aktis'' (), meaning "beam" or "ray", because of the mineral's fibrous nature.


Mineralogy

Actinolite is an intermediate member in a solid-solution series between magnesium-rich
tremolite Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro- ...
, , and iron-rich
ferro-actinoliteFerro-actinolite is the ferrous iron-rich endmember of the actinolite-tremolite continuous solid solution series of the double chain calcareous amphibole group of inosilicate minerals. All the series members belong to the monoclinic crystal system. ...
, . Mg and Fe
ion An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
s can be freely exchanged in the
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...
structure. Like tremolite,
asbestiformAsbestiform is a crystal habit. It describes a mineral that grows in a fibrous aggregate of high tensile strength, flexible, long, and thin crystals that readily separate.Committee on Asbestos: Selected Health Effects, 2006, ''Asbestos: Selected Canc ...
actinolite is regulated as
asbestos Asbestos (pronounced: or ) is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into t ...
.


Occurrence

Actinolite is commonly found in
metamorphic rock#REDIRECT Metamorphic rock#REDIRECT Metamorphic rock {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
s, such as
contact aureole upright=1.35, Schematic representation of a chlorite;_ep_=_epidote.html" style="text-decoration: none;"class="mw-redirect" title="actinolite">metamorphic reaction. Abbreviations of minerals: act = actinolite; chl = Chlorite group">chlorite; ep ...
s surrounding cooled intrusive
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lav ...
s. It also occurs as a product of
metamorphism upright=1.35, Schematic representation of a chlorite;_ep_=_epidote.html" style="text-decoration: none;"class="mw-redirect" title="actinolite">metamorphic reaction. Abbreviations of minerals: act = actinolite; chl = Chlorite group">chlorite; ep ...
of magnesium-rich
limestone Limestone is a common type of carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (). Limestone forms when these minerals precipitate out of water con ...
s. The old mineral name ''uralite'' is at times applied to an alteration product of primary
pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium, sodium, iron (II) or ...
by a mixture composed largely of actinolite. The metamorphosed
gabbro Gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
or
diabase Diabase () or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled ...
rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...
bodies, referred to as
epidiorite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase. Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz. It is ...
, contain a considerable amount of this ''uralitic'' alteration. Fibrous actinolite is one of the six recognised types of
asbestos Asbestos (pronounced: or ) is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into t ...
, the fibres being so small that they can enter the lungs and damage the Pulmonary alveolus, 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). 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.


See also

* Classification of minerals (disambiguation), Classification of minerals * List of minerals


References

* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York {{Commonscat, Actinolite Inosilicates Calcium minerals Magnesium minerals Iron(II) minerals Asbestos Amphibole group Monoclinic minerals Minerals in space group 12 Gemstones