Actinolite is a member of a series that contains varying amounts of iron and magnesium.
1 Minute Read
Comments: Actinolite is a member of a series that contains varying amounts of calcium, magnesium, iron, and aluminum, and has a chemical formula of Ca2(Mg,Fe)5Si8O22(OH)2. Tremolite is the Mg end, and ferroactinolite the Fe end, with actinolite in the middle. Actinolites with more than 50% Fe are very rare. Catseye actinolite exists (S.G. 3.0, R.I. 1.63); when chatoyant material is cut, it exhibits a fine eye. Actinolite is easy to cleave and hard to cut and would make a poor jewelry stone. Actinolite is the chief constituent of nephrite (jade). Smaragdite is a chrome-rich tremolite from Tanzania.
Name: Greek aktis, meaning ray, due to the fibrous nature.
Optics:
α = 1.619-1.622;
β = 1.632-1.634;
γ = 1.642-1.644 (Tanzanian material).
Biaxial (-); 2V = 78°
Occurrence: Contact metamorphic limestones and dolomites; magnesium-rich limestones and ultrabasic rocks; regionally metamorphosed rocks.
| Locality | Pleochroic Colors | α | β | γ | Birefringence | S.G. | Comments |
| Fowler, New York | red-violet | 1.602 | - | 1.630 | 0.028 | 3.03 | Hexagonite |
| Kenya | bright green | 1.602 | 1.613 | 1.628 | 0.026 | 2.99 | Tremolite |
| 1.607 | 1.618 | 1.632 | 0.025 | 3.01 | |||
| Tanzania (Lelatema) | yellow green/green | 1.608 | 1.616 | 1.631 | 0.023 | 3.01 | Tremolite |
| Tanzania | emerald green | 1.611 | 1.623 | 1.639 | 0.028 | 3.30 | Tremolite + Cr |
| Tanzania (Merelani) | yellow-green/emerald green | 1.608 | 1.618 | 1.63 | 0.022 | Smaragdite | |
| Taiwan | yellow-green/green tones, | 1.607- | - | 1.630- | 0.023- | 3.01 | Tremolite |
| also brownish | 1.609 | 1.633 | 0.024 | ||||
| 1.615- | - | 1.631- | 0.014- | 3.01 | Catseye tremolite | ||
| 1.619 | 1.633 | 0.016 | |||||
| Uganda | yellow-green/green | 1.619- | 1.632- | 1.642- | 0.021- | 3.04- | Tremolite-Actinolite |
| 1.622 | 1.634 | 1.644 | 0.024 | 3.07 | |||
| green/brown | 1.633 | - | 1.653 | 0.020 | 3.15 | Actinolite |
Chester, Vermont.
Madagascar: small, dark green crystals. Many of these are clean and suitable for faceting.
Tanzania: transparent crystals. (See also nephrite.)
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Comments: Actinolite is a member of a series that contains varying amounts of calcium, magnesium, iron, and aluminum, and has a chemical formula of Ca2(Mg,Fe)5Si8O22(OH)2. Tremolite is the Mg end, and ferroactinolite the Fe end, with actinolite in the middle. Actinolites with more than 50% Fe are very rare. Catseye actinolite exists (S.G. 3.0, R.I. 1.63); when chatoyant material is cut, it exhibits a fine eye. Actinolite is easy to cleave and hard to cut and would make a poor jewelry stone. Actinolite is the chief constituent of nephrite (jade). Smaragdite is a chrome-rich tremolite from Tanzania.
Name: Greek aktis, meaning ray, due to the fibrous nature.
Optics:
α = 1.619-1.622;
β = 1.632-1.634;
γ = 1.642-1.644 (Tanzanian material).
Biaxial (-); 2V = 78°
Occurrence: Contact metamorphic limestones and dolomites; magnesium-rich limestones and ultrabasic rocks; regionally metamorphosed rocks.
| Locality | Pleochroic Colors | α | β | γ |
| Birefringence |
| S.G. |
| Comments |
| Fowler, New York | red-violet | 1.602 | - | 1.630 | 0.028 | 3.03 | Hexagonite |
| Kenya | bright green | 1.602 | 1.613 | 1.628 | 0.026 | 2.99 | Tremolite |
| 1.607 | 1.618 | 1.632 | 0.025 | 3.01 |
| Tanzania (Lelatema) | yellow green/green | 1.608 | 1.616 | 1.631 | 0.023 | 3.01 | Tremolite |
| Tanzania | emerald green | 1.611 | 1.623 | 1.639 | 0.028 | 3.30 | Tremolite + Cr |
| Tanzania (Merelani) | yellow-green/emerald green | 1.608 | 1.618 | 1.63 | 0.022 | Smaragdite |
| Taiwan | yellow-green/green tones, | 1.607- | - | 1.630- | 0.023- | 3.01 | Tremolite |
| also brownish | 1.609 | 1.633 | 0.024 |
| 1.615- | - | 1.631- | 0.014- | 3.01 | Catseye tremolite |
| 1.619 | 1.633 | 0.016 |
| Uganda | yellow-green/green | 1.619- | 1.632- | 1.642- | 0.021- | 3.04- | Tremolite-Actinolite |
| 1.622 | 1.634 | 1.644 | 0.024 | 3.07 |
| green/brown | 1.633 | - | 1.653 | 0.020 | 3.15 | Actinolite |
Chester, Vermont.
Madagascar: small, dark green crystals. Many of these are clean and suitable for faceting.
Tanzania: transparent crystals. (See also nephrite.)
Actinolite is a crystal found in countries like the US, Brazil, China, and Canada. Actinolite is commonly used in industrial applications such as in the production of asbestos because it has similar properties to asbestos fibers. It is sometimes used as a gemstone, but it is not suitable for jewelry. Some types of actinolite are rare, which makes it an attractive to some collectors.
