Actinolite
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Actinolite is an inosilicate mineral with the chemical formula
Ca2(MgFe)5Si8O22(OH)2
Mineralogy
Actinolite is an intermediate member in a solid-solution series between tremolite (Mg-rich) and ferro-actinolite (Fe-rich) amphiboles. As seen from the chemical formula above, Mg and Fe ions can be freely exchanged in the crystal structure.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. Another form of actinolite, known as nephrite, is one of the two common constituents of jade (the other being jadeite).
Details
| Crystallographic system | Monoclinic |
| Colours | Pale to dark green. White or grey when in asbestos form |
| Lustre | Vitreous to dull glassy |
| Hardness | 5.5-6 |
| Refractive index | 1.61 |
| Cleavage | 2 |
| Pleochroism | Yellow to dark green to transparent to opaque |
Related minerals
References
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0471805807
- [Mindat.org]
- [Webmineral.org]
- [Mindat - uralite]
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