Actinolite is an amphibole silicate mineral 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.

Fibrous actinolite is one of the six recognized types of asbestos, the fibers being so small that they can enter the lungs and damage the alveoli. As this specimen is the fibrous version of Actinolite it should be treated with caution and viewed inside it's case only.

When inhaled, the tiny fibers stick into and cause scar tissue build up in the lungs. Asbestos is the primary cause of Mesothelioma, a rare and fatal cancer of the membrane lining the lungs and abdomen. When the link between asbestos and Mesothelioma was discovered, industry began phasing out it's use.

Asbestos regulations vary globally and often depend on the type of asbestos. Most countries, including the U.S., ban asbestos use. This includes a ban on amphibole types, like crocidolite and amosite. Some exemptions remain for chrysotile asbestos. It is allowed in certain products under specific conditions in the U.S. and Canada.

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.