Actinolite

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Actinolite
Actinolite crystal in matrix from Finland
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.

Contents 1 Mineralogy 2 Occurrence 3 Gemology 4 References

[edit] 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.

[edit] 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.

[edit] 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]

[edit] 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

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
• Mindat.org
• Webmineral.org
• Mindat - uralite

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