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Actinolite

Actinolite
General
Chemical formula Ca2(Mg,Fe)5Si8O22(OH)2[1]
Identification
Color Pale to dark green, yellowish green and black.[2] White or grey when in asbestos form
Crystal habit bladed, fibrous, radial
Crystal system Monoclinic[2]
Twinning simple or lammelar
Cleavage Perfect in two directions. [2]
Fracture uneven[2]
Mohs Scale hardness 5 - 6[2]
Luster vitreous to dull[2]
Polish luster vitreous [2]
Refractive index 1.606 - 1.641 (+.014)[2]
Optical Properties Double refractive with anomalous aggregate reaction, biaxial negative.[2]
Birefringence .022 - .027[2]
Pleochroism moderate, yellow to dark green (in stones that are transparent)[2]
Ultraviolet fluorescence inert[2]
Absorption spectra faint line at 503nm[2]
Streak white
Specific gravity 3.00 (+.10, -.05)[2]
Diaphaneity translucent to transparent

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

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).[2]

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.[2] Transparent actinolite is rare and is faceted for gem collectors.[2] Major sources for these forms of actinolite are Taiwan and Canada.[2] Other sources are Madagascar, Tanzania, and the US.[2]

References

1. ^ http://rruff.geo.arizona.edu/doclib/hom/actinolite.pdf Mineral Handbook
2. ^ a b c d e f g h i j k l m n o p q r s (Gia), Gemological. Gem Reference Guide. City: Gemological Institute of America (GIA), 1988. ISBN 0-87311-019-6



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