| Actinolite | |
|---|---|
 Actinolite crystal fromPortugal | |
| General | |
| Category | Inosilicates |
| Formula | Ca2(Mg4.5-2.5Fe2+0.5-2.5) Si8O22(OH)2 |
| IMA symbol | Act[1] |
| Strunz classification | 9.DE.10 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | C2/m |
| Identification | |
| Color | pale to dark green, yellowish green, blue and black. White or grey when in asbestos |
| Crystal habit | bladed, fibrous, radial |
| Twinning | simple or lamellar |
| Cleavage | perfect along {110}. |
| Fracture | uneven |
| Mohs scale hardness | 5–6 |
| Luster | vitreous to dull |
| Streak | white |
| Diaphaneity | translucent to transparent |
| Specific gravity | 3.00 (+0.10, -0.05) |
| Polish luster | vitreous |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.613–1.628 nβ = 1.627–1.644 nγ = 1.638–1.655 |
| Birefringence | 0.0250–0.0270 |
| Pleochroism | moderate, yellow to dark green (in stones that are transparent) |
| 2V angle | 78–82° (calc), 84–73° (meas) |
| Dispersion | r < v |
| Ultravioletfluorescence | inert |
| Absorption spectra | faint line at 503 nm |
| References | [2][3][4][5][6] |
Actinolite is anamphibolesilicate mineral with the chemical formulaCa2(Mg4.5–2.5Fe2+0.5–2.5)Si8O22(OH)2.
The nameactinolite is derived from theGreek wordaktis (ἀκτίς), meaning "beam" or "ray", because of the mineral's fibrous nature.[3]
Actinolite is an intermediate member in asolid-solution series between magnesium-richtremolite,Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2, and iron-richferro-actinolite,☐Ca2(Mg2.5-0.0Fe2+2.5-5.0)Si8O22(OH)2. Mg and Feions can be freely exchanged in thecrystal structure. Like tremolite,asbestiform actinolite is regulated asasbestos.
Actinolite is commonly found inmetamorphic rocks, such ascontact aureoles surrounding cooledintrusiveigneous rocks. It also occurs as a product ofmetamorphism of magnesium-richlimestones.
The old mineral nameuralite is at times applied to an alteration product of primarypyroxene by a mixture composed largely of actinolite. The metamorphosedgabbro ordiabaserock bodies, referred to asepidiorite, contain a considerable amount of thisuralitic alteration.
Fibrous actinolite is one of the six recognised types ofasbestos, thefibres being so small that they can enter thelungs and damage thealveoli. Actinolite asbestos was once mined along Jones Creek atGundagai, Australia.
Some forms of actinolite are used asgemstones. One isnephrite, one of the two types ofjade (the other beingjadeite, a variety of pyroxene).[5]
Another gem variety is thechatoyant form known ascat's-eye actinolite. This stone is translucent to opaque, and green to yellowish green color. This variety has had the misnomerjade cat's-eye. Transparent actinolite is rare and is faceted for gem collectors. Major sources for these forms of actinolite areTaiwan andCanada. Other sources areMadagascar,Tanzania, and theUnited States.[5]
