Olivine is a kind of island-structured silicate mineral with the chemical formula
(Mg, Fe)2[SiO4], containing trace elements Mn, Ni, Ca, and Al , Ti et al. It belongs to the orthorhombic crystal system. The crystal shape is often short columnar, and the aggregates are mostly irregular granular. The color is mostly olive green, yellow green, golden green or emerald green. Glassy, ??transparent. The refractive index is 1.654-1.690, and the birefringence is 0.035-0.038. The pleochroism is not obvious and the dispersion is 0.020. Hardness 6.5-7.0, density 3.27-3.48 g/cubic centimeter. It is brittle, has poor toughness, and is prone to cracks.
R in the chemical formula is mainly divalent cations magnesium, iron, and manganese. Among them, the magnesium-rich magnesium ferroolivine is the most common and is generally called olivine. Gem-grade ones are light green-yellow, yellow-green (olive green), green-brown, and brown. The color and pleochroism change with the iron content. Those with light color do not show pleochroism, those with predominantly green color show green-weak green-yellow-green trichromaticity, while those with predominantly brown color show trichromaticity of brown-light brown-dark brown. Glassy, ??transparent. The starlight effect or cat's eye effect is rare.
The biaxial crystal is positive, but contains excess iron and becomes negative. The refractive index is generally between 1.654 and 1.690. The birefringence is 0.035-0.038. From the countertop of the faceted stone, you can see the double shadow of the pavilion and the double shadow of the inclusion. Dispersion (0.020) is medium.
Under ultraviolet light, olivine has no fluorescence reaction. Green under the Charles filter. The characteristic absorption spectrum is three narrow absorption bands at 433 nm, 474 nm and 497 nm in the blue area. The two groups of 100 and 0101 have incomplete cleavage and conchoidal fractures. The hardness is 6.5 to 7, and the toughness is medium to good. Density: gem grade is 3.34g/cm3. It is highly heat sensitive and can easily break when heated unevenly or rapidly. Quickly reacts with HCI, HF or concentrated and hot H2SO4; cannot be cleaned with any acid or alkali solution.
Microscopic characteristics: Gem-quality olivine is basically formed from magma. Its typical inclusions include lava glass beads of different sizes and round, oblate, and lotus leaf-shaped residues (magma ) The gas-liquid film surrounds the characteristic "lily pad" or crinoid-like inclusions formed by chromite microcrystals or negative crystals (chromite microcrystals or negative crystals, with star-like bundles of veins distributed around them) like bursting cracks). Separate mineral guest crystals, in addition to chromite, also include brown to brownish red chromium spinel, reddish-brown biotite, chromium diopside, graphite, etc. The constituent material of olivine is also one of the main constituent minerals of mantle rocks. Various ejected or intruded basic and ultrabasic rocks in the earth's crust related to mantle materials contain large amounts of olivine.
During contact metamorphism and regional metamorphism, magnesian carbonate rock layers will be transformed into olivine due to metamorphism.
Metamorphic ferruginous sediments and dolomitic limestones are composed entirely of olivine. Olivine is also one of the main minerals that make up stony meteorites.
Olivine and quartz do not occur independently, so there is no olivine in neutral rocks or acidic rocks. 1． Crystal system and crystallization habit.
Orthorhombic crystal system: The crystals are mostly in the shape of short columns or thick plates. Common simplex shapes have parallel sides.
Rhomboidal cylinder and rhomboidal double pyramid. Gem-quality peridots are mostly irregular columnar shapes and rare ones are intact.
2. Color and pleochroism, mainly yellow-green, with a small amount of brown-green or brown. Weak pleochroism.
3． Gloss and Transparency: Glassy gloss, transparent to translucent.
4. Optical properties: Biaxial crystal, the positive and negative optical properties depend on the composition.
5. Refractive index and birefringence: RI: 1.65-1.69, RI: 0.036, the brown variety is slightly higher.
6. Dispersion: 0.020, medium.
7. Absorption spectrum: three absorption bands in the blue area: 453nm, 473nm, and 493nm.
8. Hardness: 6.5-7, changes with changes in ingredients.
9． Relative density: 3.32-3.37, varies depending on composition.
10. Cleavage and fracture: poor cleavage, conchoidal fracture.
11. Inclusions
Mineral inclusions are common in olivine. These solid inclusions are often accompanied by disc-shaped stress lines or gas-liquid packets, which are called "lily pads" "like inclusions, in addition to reddish-brown biotite, chromium diopside, graphite, calcite, etc., zircon halos, negative crystals, cloud-like inclusions, etc. can also be seen. The world-famous origins of high-quality olivine include Brazil, Egypt's St. John's Island in the Red Sea, Mount Vesuvius in Italy, Snarum in Norway, the Eifel region in Germany, Arizona and New Mexico in the United States, etc. Gem-quality olivine was discovered in the Hannuoba basalt xenoliths in Zhangjiakou, Hebei, China.
Olivine is the main component of mantle rocks and is widely produced in various basic and ultrabasic rocks and magnesian carbonate metamorphic rocks. Most of the world's olivine is produced in alkaline basalt deep source inclusions and spinel lherzolite. The olivine produced in Hebei and Jilin in my country belongs to this type of production. There is also a small amount of olivine occurring in veins in the peridotite.
Brazil, Australia, Norway, Pakistan, and the Red Sea Island of Sebut in Egypt are famous origins of high-quality olivine. Other well-known producing areas are Australia, Brazil, Kenya, Tanzania, Norway, Sri Lanka and Myanmar; Myanmar was also a famous olivine producing country and also produced some large-grained olivines. The former Soviet Union and the Czech Republic also produce some olivine.
The raw stone is produced in serpentinized peridotite nickel veins. High-quality giant peridot gemstones are produced near Mogok, Myanmar. The olivine deposit on the northern border of Mexico is one of the largest olivine deposits in the world. The olivine is brown. Peridots from Maping, Wanquan County, Hebei, and Dashi River, Zhihe, Jilin, China are green to yellow-green in color.
Peridot from San Carlos, Arizona, USA, is the largest source of gem-quality olivine; olivine with trace amounts of chromium and beautiful color is produced on the coast of Hawaii; the ancient famous origin of Zebargad in Egypt has not produced much. However, olivine has a large particle size, and gemstones of several centimeters are still produced.
my country's two well-known olivine producing areas are both basalt-type inclusions. The output in Zhangjiakou, Hebei, is greater than that in Jiaohe, Jilin. The particle size of Zhangjiakou Cannaping olivine is generally 5-7 mm, with the largest being 34 mm x 20 mm x 15 mm, and it is olive green or yellow-green. The particle size of Jiaohe Baishishan olivine is mostly 5-8 mm, and the larger ones are generally 10-20 mm. The absorption curve study shows that the main color is yellow, with a green-yellow or yellow-green appearance.