Definitions

actinolite

actinolite

[ak-tin-l-ahyt, ak-tuh-nl-]
actinolite: see amphibole.

Colourless to green amphibole mineral, darkening with increased iron content from green to black. It has a prismatic and splintery texture and is abundant in regionally metamorphosed (see metamorphism) rocks such as schists. Actinolite has a monoclinic crystal structure, and it may alter to chlorite. Seealso asbestos.

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For the community in Canada see Actinolite, Ontario. For the Sailor Moon character, see Shitennou (Sailor Moon).

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

Mineralogy

Actinolite is an intermediate member in a solid-solution series between tremolite (Mg-rich) and ferro-actinolite (Fe-rich) amphiboles. As seen from the chemical formula above, 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. The first is called nephrite, which is one of the two types of jade (the other being jadeite a variety of pyroxene).

Another gem variety of actinolite 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 US.

Related minerals

  1. Tremolite
  2. Jade

References

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