Comments: Actinolite is a member of a series that contains varying amounts of iron and magnesium. 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 |
Chemical composition vs. optics and density of common hornblendes.
Adapted from W.A. Deere, R.A. Howie, and J. Zussman, 1962, The Rock Forming Minerals, vol.2 (New York: Wiley), p.296.
Chester, Vermont.
Madagascar: small, dark green crystals. Many of these are clean and suitable for faceting.
Tanzania: transparent crystals. (See also nephrite.)
