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).Mineralogy
Actinolite is an intermediate member in a series between tremolite (Mg-rich) and ferro-actinolite (Fe-rich). 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 is also found in magnesium-rich limestones.
| 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 |