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Actinolite
Chemical Formula	Ca2(Mg,Fe)5Si8O22(OH)2
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	5-6
Specific Gravity	3.00
Color	pale to dark green, yellowish green and black. White or grey when in asbestos form
Streak	white
Luster	Vitreous, Silky
Refractive Index	n = 1.613 - 1.646 n = 1.624 - 1.656 n = 1.636 - 1.666
Diaphaneity	Transparent, Translucent
Cleavage	Distinct/Goodon
Fracture	Splintery
Crystal Habit：bladed, fibrous, radial
Geological Setting：Produced by low-grade regional or contact metamorphism of magnesium carbonate, mafic, or ultramafic rocks; Also in glaucophane-bearing blueschists. Occurs in many localities. In Austria, on Mt. Greiner, Zillertal, and at Untersulzbachtal. From Zermatt, Valais, Switzerland. At Snarum and Arendal, Norway. From the Ural Mountains, Russia. In the USA, from Gouverneur, St. Lawrence Co., New York; Franklin and Newton, Sussex Co., New Jersey; Chester, Windsor Co., Vermont; in the Fairfax quarry, Centreville, Fairfax Co., Virginia; Crestmore, Riverside Co., California; at Salida, Cha?ee Co., Colorado. Nephrite jade occurs, in the USA, south and east of Lander, Fremont Co., Wyoming; north from Cape San Martin, Monterey Co., California; and around Jade Mountain, near the Kobuk River, Alaska. Along the Fraser River, British Columbia, Canada. Around Mt. Cook, South Island, New Zealand. Fine material from the Kunlun Mountains, Sinkiang Uighur Autonomous Region, China.

Etymology

The name actinolite is derived from the Greek word aktis (?κτ??), meaning "beam" or "ray", because of the mineral's fibrous nature. (This word is also the origin of the name of the chemical element actinium.)

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.

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).

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.