The English name actinolite originates from the Greek word Aktis (radiation), emphasizing that this mineral is often in bundle and radial aggregates.
The Chinese name “阳起石” emphasizes the effect of warming the kidney and strengthening the yang of this mineral, which is a mineral medicine in ancient Chinese medicine and is still used today.
Actinolite belongs to the amphibole group of minerals, which is a metamorphic mineral formed in the rich-Iron environment and produced in greenschist such as gneiss, phyllite, chlorite, talc, serpentine, etc.
Actinolite minerals are widely distributed, but gem-grade crystals are very rare. The Main producing areas are Madagascar, Tanzania, the United States, Canada, China, etc.
Actinolite and other minerals are aggregated into a block, which can be used as jade carving materials. Its fiber structure crystal can be ground into a cat’s eye effect gem.
- Monoclinic system
- Crystals are flat columnar, needle-shaped, or fibrous, often producing radioactive aggregates.
- The color is mainly grayish green to dark green, but also yellow, purple and brown.
- Transparent to translucent;
- glass luster.
- Biaxial negative crystal,
- Refractive index: 1.61~1.64,
- Birefringence: 0.022~0.027,
- Relative density: 3,
- Mohs hardness: 5~6.
Basic properties of actinolite
Chemical formula: Ca2 (Mg, Fe3+) [Si4On] 2 (OH, F) 2, actinolite contains more Fe2+ than tremolite, and the M value is 0.9~0.5. If the M value is less than 0.5, it is Ferro-Actinolite.
Form: monoclinic system. The crystals are long columnar and needle-lie, and the aggregates are radial and fibrous.
Photometric: It is bright green, brown-green, yellow, and other colors, generally not black, green black; It is Light-green in thin slices.
Weak polychromatic: Ng=green, light green, Nm=light yellow-green, Np=light yellow. Np=1.619~1.688,Nm=1.630～1.697，Ng=1.640～1.705。 With the increase in iron content, the polychromatic becomes more obvious, and the refractive index also increases. Ng-Np=0.023～0.027.
Others: The highest interference is Grade II blue – Grade II green. Monocline amphibole extinction type, Ng ^ c=10 °～ 15 °.
Simple twins and polycrystalline twins are common. Two axis (I), 2V=65 °~83 °. The optical orientation is similar to that of tremolite.
Where is Actinolite From
Actinolite often occurs near the metal ore vein, which is formed by high-temperature hydrothermal alteration of augite and diopside in early skarn and basic and neutral magmatic rocks and is often associated with epidote.
In addition, actinolite also occurs in the crystalline schist of greenschist facies. Actinolite is also the main rock-forming mineral of Hetian jade.
How to identify actinolite
It is different from tremolite in light green, weak polychrome, and small extinction angle. Cryptocrystalline dense massive actinolite or tremolite is called Hetian Jade. It can be seen under the microscope that Hetian Jade is composed of numerous actinolite or tremolite crystals interlaced into a felt shape.
Comparison between actinolite and common amphibole
Actinolite is easily mixed with ordinary amphibole; what is their difference?
The amphibole family has a double-chain silicate structure in the crystal structure, silicates containing hydroxy groups of magnesium, iron, calcium, sodium, and aluminum (characterized by metasilicate with [SiOn]6-).
According to the different ownership of crystal systems, it can be divided into three subgroups: orthorhombic amphibole, monoclinic amphibole, and triclinic amphibole.
The orthorhombic amphibole subfamily mainly includes amphibole and gedrite;
The subgroups of monoclinic amphibole mainly include tremolite, actinolite, common hornblende, glaucophane, and arfvedsonite;
The subgroups of triclinic amphibole include enigmatite and rhoenite. Although these amphiboles’ chemical composition and crystal system are different, they have many similar properties.
Its crystals are mostly in the form of long columns, needles, or fibers. The cross-section of the crystals ranges from rhombus to hexagon.
The aggregates are granular, fascicular, and radial. The hardness is 5-6, the cleavage parallel rhombic column (110) is medium, the two groups of cleavage intersect into 56 ° or 124 °, and the relative density is 2.90-3.50.
Generally, it has glass luster, Transparent to opaque. The color varies according to the variety and impurities contained.
The optical property varies slightly with varieties, so it can be used as the primary indicator to identify different varieties.
Amphibole group minerals are one of the critical rock-forming minerals. Ordinary amphibole is widely distributed in neutral and intermediate acid igneous rocks, and it is also the main component mineral of many metamorphic rocks.
Tremolite and actinolite are important products of contact metasomatism. Sodium-rich alkaline amphibole is the main mineral of alkaline rocks.
Among these numerous amphibole group minerals, tremolite, actinolite, and nephrite composed of them are known to have gem jade value.
In addition, dark black ordinary amphibole crystals are also expected to become a potential source of black gemstones. In industry, people mainly use fibrous amphibole, the so-called amphibole asbestos.
The difference is:
- The actinolite is light green in thin slices, and its pleochroism and absorbability are weaker than ordinary amphibole.
- Actinolite is never brown in thin slices, while ordinary amphibole can be green or brown. If it is brown, it is not actinolite but ordinary amphibole.
- The refractive index of actinolite is generally lower than that of ordinary amphibole, while the birefringence is generally higher than that of ordinary amphibole.
Actinolite cat’s eye
If actinolite aggregates with parallel fiber structure, the cat’s eye effect can appear when the convex arc-shaped gem is ground.
Its body color is mostly green with yellow, brown, and gray tones. The cat’s eye is not clear due to its low definition, but it is enough “pointy” to be an attractive gem. The disadvantage is that it is easy to appear linear crack and is not as durable as other opals.
These gemstones have been found in Taiwan, Sichuan, China, British Columbia, Canada, and Alaska, the United States (in fact, it is difficult to distinguish them from tremolite cat’s eyes, it is appropriate to collectively call it “nephrite cat’s eye”).
The name of gem is consistent with that of mineral. Actinolite gemstone is mostly dark green or green-black, generally very small. All known are within 10 carats. Cat’s eye actinolite was very small, only 1-2 carats.
The actinolite gem from Madagascar is dark green and translucent. The actinolite gems from Tanzanian are completely clear and transparent, with the best quality.