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Olivine in Earth’s Mantle
Olivine is thought to be an important mineral in Earth’s mantle. Its presence as a mantle mineral has been inferred by a change in the behavior of seismic waves as they cross the Moho – the boundary between Earth’s crust and mantle. The presence of olivine in Earth’s interior is also confirmed by the presence of olivine…
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Composition of Olivine
Olivine is the name given to a group of silicate minerals that have a generalized chemical composition of A2SiO4. In that generalized composition, “A” is usually Mg or Fe, but in unusual situations can be Ca, Mn, or Ni. The chemical composition of most olivine falls somewhere between pure forsterite (Mg2SiO4) and pure fayalite (Fe2SiO4). In that…
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Geological Occurrence of Olivine
Most olivine found at Earth’s surface is in dark-colored igneous rocks. It usually crystallizes in the presence of plagioclase and pyroxene to form gabbro or basalt. These types of rocks are most common at divergent plate boundaries and at hot spots within the centers of tectonic plates. Olivine has a very high crystallization temperature compared to other minerals. That…
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What is Olivine?
Olivine is the name of a group of rock-forming minerals that are typically found in mafic and ultramafic igneous rocks such as basalt, gabbro, dunite, diabase, and peridotite. They are usually green in color and have compositions that typically range between Mg2SiO4 and Fe2SiO4. Many people are familiar with olivine because it is the mineral of a very popular green gemstone known as peridot.
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Determining Green Color Origin
Anyone who contemplates spending significant money on a green diamond should purchase the diamond from a business that has a reputation for selling colored diamonds. In addition, the diamond and the cause of its color should be evaluated by a trusted laboratory. Two questions are important: 1) is the diamond natural or synthetic; and, 2)…
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Famous Green Diamonds
Two of the most famous and valuable natural-color green diamonds are the “Aurora Green” and the “Dresden Green.” The Aurora Green In 2016, a ring containing the Aurora Green, a 5.03-carat, VS2 clarity, Fancy Vivid green diamond, was sold at a Christie’s auction for $16.2 million. That was the highest price ever paid for a…
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Are Irradiated Diamonds Safe?
Because many green diamonds obtain their color from exposure to radiation in a laboratory (a process known as irradiation), there have been concerns about their safety when used in jewelry. All companies in the United States that apply radiation treatments to any type of gemstone must be licensed by the Nuclear Regulatory Commission. These companies must use…
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What Causes the Color of Green Diamonds?
A) Formation of Natural-Color Green Diamonds Diamonds with a natural green color developed that color while they were underground, in rocks that contained small amounts of radioactive material such as uranium or thorium. As the radioactive materials decayed, they emitted radiation that penetrated the nearby diamond crystal. When this type of radiation enters a diamond, it can…
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Natural Green Color in Diamonds
In many green diamonds, the color is confined to a thin layer at the surface of the rough stone. The design and cut of the polished diamond must be carefully planned and executed to conserve as much of that original color as possible. Even though the faceting might only preserve a band of green color…
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Have You Seen a Green Diamond?
Natural-color green diamonds are very rare. Of all diamonds cut into polished gems in any given year, a very small number of them will have a dominant green color. Diamonds with a natural green color are rare enough that many people have never seen one, and those who have seen one are likely to have seen it…