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Chemical Formula | Ca2(Mg,Fe)5Si8O22(OH)2 | ||
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Composition | Basic calcium, magnesium, iron silicate | ||
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Color | Light to dark green; grayish green to black. | ||
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Streak | Colorless | ||
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Hardness | 5½ - 6 | ||
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Crystal Forms and Aggregates |
(Monoclinic) Occurs as elongated prismatic crystals, bladed, columnar, fibrous, and acicular. Also occurs radiating, as wheat sheaf formations, and as tough interlocking fibers which may appear massive. The fibrous variety is flexible and elastic. | ||
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Transparency | Translucent | ||
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Specific Gravity | 2.9 - 3.5 | ||
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Luster | Vitreous, silky | ||
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Cleavage | 2,2 - prismatic | ||
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Fracture | Uneven and/or splintery | ||
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Tenacity | Brittle. Some fibrous specimens are elastic. | ||
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Varieties | Note: Some of these varieties are also
varieties of other amphibole minerals. Amianthus
- Old name applied to any asbestos (i.e. fibrous) mineral of the amphibole group Asbestos
- Any extremely fibrous mineral. When applied to Actinolite, it
refers to the fibrous variety. Asbestos
Amphibole - Term applied to any fibrous mineral of the amphibole group, including Actinolite Byssolite
- Actinolite or Tremolite composed of tiny, interwoven, fibrous crystals; creating a tough mass Ferro-actinolite
- Variety of Actinolite where the magnesium is wholly
replaced by iron Mountain
Leather or Mountain Cork - Name
applied to fibrous minerals of the amphibole group composed of a mat-like felt of fibers that look and feel like knitted cloth. Nephrite - Variety of Actinolite/Tremolite
made up of tough, hard, interwoven fibers. The content of iron and magnesium are
about equal in Nephrite. Uralite
- Pseudomorph of Actinolite after a mineral of
the pyroxene group |
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In Group | Silicates ; Inosilicates ; Amphibole group | ||
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All About | Actinolite gets its green color from the
presence of iron in its structure. The amount of iron varies among specimens,
causing different contrasts of green. If a mineral has
less than two percent of iron in the structure (which is
replaced by magnesium), then it is not Actinolite, but Tremolite. Actinolite and Tremolite share
the same chemical formula, but Actinolite has a greater
presence of iron over magnesium, whereas Tremolite has a
greater presence of magnesium over iron. Because they
share the same formula, there are varieties that belong
to both of them. Mountain Leather, a fibrous varieties of Actinolite, has a silky luster, a soft felt-like feel, and elastic fibers. Nephrite, another fibrous variety, is made up of tough, interlocking fibers, so dense that the fibers are not discernible. Any translucent Nephrite specimen that has an interesting or uniform color distribution and is extremely tough fits under the category of Jade. Actinolite sometimes occurs as thin, splintery inclusions inside Quartz crystals. If the inclusions are parallel and dense, chatoyancy will be seen. Asbestos Actinolite should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma (an inoperable cancer of the chest and abdominal lining). Symptoms of asbestosis do not arise until about 20 years after the inhalation. Washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos because of the hazards. |
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Uses | The finely fibrous variety of Actinolite is
used for industrial asbestos. Although fibrous Serpentine is the main source of asbestos,
Actinolite is a great contributor. Because it is not
affected by fire and is a poor heat conductor, it is used
in fire retardant devices and for heat protection. Its
former use, which has been outlawed in most areas, was as
an insulator, but has been banned because of its
notorious nature of causing cancer and other long term
illnesses. Nephrite is one of the minerals that form the important gem Jade. Jade is cut into cabochons, beads, and earrings. Rings and bracelets are sometimes carved out of an entire mass of Jade. Valuable ornamental sculptures and figures are also carved from this gem. Nephrite is only one form of Jade; the other form is the more valuable Jadeite. |
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Striking Features | Green color, crystal habit, and cleavage angle of amphiboles | ||
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Complex Tests | Insoluble in acid | ||
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Popularity (1-4) | 2 | ||
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Prevalence (1-3) | 2 | ||
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Demand (1-3) | 1 | ||
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Distinguishing Similar Minerals |
Tourmaline - lacks cleavage, harder (7 - 7½) Wollastonite - softer (4½ - 5), different cleavage angle, usually fluorescent Epidote - different cleavage angle, crystals are more glassy Tremolite - no distinction can be made without x-ray equipment |
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Commonly Occurs With |
Albite, Barite, Chlorite, Epidote, Muscovite, Serpentine, (Marble) | ||
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Noteworthy Localities |
There are several localities where good
Actinolite specimens can be obtained, but only the finest
will be mentioned. It is been found in the Moonta and
Wallaroo mines in Western Australia; Tyrol, Austria, and
Bahia, Brazil. In North America, it occurs in Mont Saint
Hilaire, Quebec (Canada); Chester, Windsor Co., Vermont;
the French Creek Mine, Chester Co., Pennsylvania;
Sanford, York Co., Maine; Hopland, Mendocino Co.,
California; and Pleasanton, Alameda Co., California. See also Nephrite for additional localities. |
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Picture Icon Links |
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Picture Links | 1. Actinolite crystal bundle |
