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Actinolite
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.
Actinolite
Value
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Actinolite is rarely facetable and usually in small fragments. Material from Chester, Vermont, could provide stones to about 10 carats. DG: 2.06 (greenish, step cut, Africa)
Yellow to dark green. Material transparent to nearly opaque.
α: pale yellow/ yellowish-green.
β: pale yellow-green/green.
γ: pale green/ deep greenish blue.
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.)
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