Extinction of Light
This is a way to look at the amount of light that is absorbed by the same gemstone such as Elbaite with different chromophores. It can also be discussed under the term tone.
extinction The dark gray to black portion of a face-up gemstone that does not refract light; usually caused by off-axis refraction.
eye The finest gemstone in a parcel.
Extinction: an area of a transparent gemstone where the body color looks
very dark to black. This occurs when gemstones are cut with excessively
deep pavilions.
Zoning ...
mass extinction
Mass extinction is the process in which huge numbers of species die out suddenly. The dinosaurs (and many other species) went extinct during the K-T extinction, which was probably caused by an asteroid colliding with the Earth.
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Extinction...Diminution in the intensity of radiation due to absorption by or scattering in the medium; also the stopping of incident X-rays by the outer layers of atoms in a crystal.
Extinction - Dark or black spots in a colored stone.
Eye-clean - A gemstone where the flaws cannot be seen without a 10-power loupe.
Next page ...
Extinction Happens
MIT geologist Sam Bowring muses on mass extinctions and why we can't take Earth's hospitable climate for granted.
Tracking Twisters With Radar ...
background extinctions
Background extinctions are those extinctions that occur continually throughout time.
Interestingly, Iridium is thought to be more common in extraterrestrial matter than on Earth, and is the most important piece of evidence linking the extinction of the dinosaurs with an asteroid strike because of its high concentration in the K-T ...
This red glow is key, for it tends to cover up the dark areas of the stone caused by extinction from cutting. Thai/Cambodian rubies might possess a purer red (less purple) body color, but they lack the strong fluorescence.
The most basic stage of judging a cut starts from ruling out visible flaws such as windowing or extinction. A widow is a see through washed out area on the facet of gem that is a result of improper faceting. A large visible window denotes poor cut.
Conch pearls are products of a large marine snail, the queen conch, It is native to the Caribbean and, until it was fished to near extinction, was found abundantly in the waters of the Florida Keys.
Extensive diving had led to the threat of extinction of these oysters but thanks to Tahiti government's initiative the black pearls started getting cultivated in professional farms around the island and the diving for gain was banned.
The composition of a plagioclase feldspar is typically denoted by its overall fraction of anorthite (%An) or albite (%Ab), and readily determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction ...
Ivory is becoming increasingly rare as the animals that produce it are endangered or near extinction. As a sacred bone it should be revered, as it has great spiritual significance.
Similarly, if the gem is cut too deep, light from above passes out the side, creating areas of darkness, known as extinction. Again, brilliance suffers (and there’s nothing worse than suffering brilliance).
Some Thai rubies have black reflections, a phenomenon called extinction, which can make their color look darker than it really is. But Thai rubies can also have a rich vivid red that rivals the Burmese in intensity.
Ivory A hard, smooth, white material from the tusks of elephants and sea mammals, used for beads and carved into statues. Harvesting ivory is illegal due to the near extinction of these animals.
It has been used throughout history for beads and other decorative items but with the possible extinction of many of the animals it has been traditionally ‘harvested' from it is now illegal to trade in new ivory.
Formerly prized for carvings, piano keys, and other items, ivory has been widely banned over the past couple of decades due to the risk of extinction of its donor species. Ancient, fossilized ivory is sometimes seen.
The Audubon society was actually founded to combat the extinction of birds sacrificed for the purposes or ornamentation.
It is found growing plant-like on the sea-bottom. With pollution on the rise everywhere it is becoming increasingly rare, to the extent that even the most prized, the Mediterranean coral, is threatened with extinction.
 See also: Color, Stone, Gemstone, Jewel, Gem
  
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